Kingambit is very strange to talk about. There are a lot of working parts to this Pokemon that make it as powerful as it is. By itself, it comes packed with incredibly flexible bulk, powerful priority, and a great STAB combination. Though, its Speed tier really complicates this a lot, especially with its common weaknesses; by itself, Kingambit would likely cement itself a very solid niche on offense due to its naturally good resistance profile and great cleaning ability, but I highly doubt it would be in discussion for a suspect, much less for the best Pokemon in the tier.
However, this is not really the case as we all know. Kingambit is the personification of Tera's attributes that can make it such a powerful mechanic, but also their potential setbacks. It's for that reason I sort of view Kingambit as a poster child for Tera's functionality in the tier. Tera leverages and enables Kingambit's innate strengths by allowing it to use its natural bulk, STABs, and damage-dealing ability in a greater range of matchups without its exploitable weaknesses being as egregiously in the equation. Tera greatly emphasizes the role Kingambit plays with its tools (stats, movepool, STABs, etc) and in this regard I believe the best way to evaluate Kingambit is to ascertain if these natural tools are powerful enough in their own right to warrant banning it with Tera to leverage them. Thinking about it like this, I feel as though if you are anti-Tera, you're going to err closer on the side of Kingambit being broken with Tera, but if you're pro-Tera, then you probably won't see Kingambit as that big of a problem. Based on what I've seen across the Policy Review thread regarding Tera and those who have vocalized their opinion on Kingambit this seems roughly true.
Thinking about the fundamentals of Kingambit's kit, it's not really its trading ability that makes it an S-tier threat. The tier has its share of solid tanks that tend to take trades like Ursaluna and Gholdengo. Instead, it is powerful priority in tandem with its bulk that makes it as potent as it is, allowing it to not only force an advantage more easily, but also allowing it to outright clean. Kingambit lives and dies by Sucker Punch.
As such, having Pokemon that can respond to the move in a vacuum is the primary way by which Kingambit can be handled on more offensive structures. Encore usage is fairly common in part to Kingambit's Sucker Punch, for example, and Enamorus/Iron Valiant are very common revenge-killing options that can either force damage on Kingambit post-Tera or outright remove it. Having tools to respond to its reliance on Sucker Punch like status, the aforementioned Encore, offensive Sucker Punch resistances, and naturally physically bulky Pokemon (Great Tusk, Zamazenta, Landorus-T, Dondozo, etc) generally makes it manageable to some degree for most structures that isn't particularly demanding since the range of conditions Kingambit needs fulfilled are a bit tricky to work around if you want it to truly dominate games. There are a wealth of Pokemon and moves in the tier that can check Kingambit in some way, shape, or form due to its reliance on Sucker Punch, and that's a commonality regardless of how Kingambit uses Tera. It requires your respect, but rarely will that endgame behemoth be a threat out the gate, especially without Supreme Overlord boosts. However there is an argument to be made for Kingambit being potentially oppressive in this regard. It's extremely feasible to check but because of Tera, you do need to allocate resources in-battle to account for it and its endgame potential, arguably to an extent that is unreasonable when you also have to account for Pokemon like Iron Valiant, Dragapult, or Baxcalibur that are frequently paired with it.
I personally feel as though Kingambit, while a top tier Pokemon, provides more for the tier than takes. Its bulk, initial resistance profile, and access to strong priority I view as a net positive in spite of its exacerbated strength with Tera, giving teams an easy reactive tool that is capable of tanking hits with Tera to consistently respond to highly dangerous Pokemon while being threatening in its own right. In this regard I view Kingambit as comparable to Melmetal in the sense that its bulk and revenge killing ability can consistently be a resource regardless of the matchup. I think that can be really valuable in volatile metagame landscapes, especially when the Pokemon in question requires skill, positioning, and matchup awareness to pilot to its full potential.
The metagame has a lot of room to grow and some things need to change, there is no doubt about that. However I personally believe that Kingambit isn't exactly apart of that problem even though it can be very powerful and overly commanding at times. It is, overall, a skill-based Pokemon because of its dynamic with Tera, its Speed tier, and Sucker Punch. Even if it can feel cheap sometimes it's often strong positioning and resource management beforehand that lead to that dominating position. DNB from me.
I'm literally seen as super pro-Tera and I want Kingambit banned, and anyone pro-Tera should. Because Kingambit is a Pokemon that gets so buffed by Tera that it is truly exclusive.
You keep Tera and lose Kingambit, or you leave Tera and take Kingambit back. This is mutually exclusive. Pro-Tera should acknowledge that Kingambit is a Pokemon that is in a prime spot to abuse Tera, with immense natural bulk, a free Choice Band boost at endgame off of that massive attack stat, priority and all the tools it needs to lead 50/50s, including Tera Blast.
And this is not about what will be done about Tera, no restriction to nerf Kingambit in the future, what should be done?
The "skill" argument is so funny because we only got there after months where the entire metagame has had to check Kingambit. People running moves on things like even Glowking trying to punish a free Kingambit switch-in, things like Moltres going PhysDef even when that's frankly mid outside of fishing for Burn.
Something to note is this tier has quite a few physical Attackers, not really. Some common Iron Valiant sets, Kingambit, Sneasler, Roaring Moon, Baxcalibur, Ursaluna, Samurott-Hisui technically, Azumarill exists I guess,
And yet, almost all the prep is specifically for Kingambit, and most of the ways people try to check "Physical Attackers" is specifically actually just, Kingambit. Will-O-Wisp is a good move of course, but the Pokemon running it don't exactly do a good job of checking the other Physical Attackers. Baxcalibur clicks Dragon Dance and outspeeds Cinderace, plus the obvious ability, Roaring Moon as well, Ursaluna is already burned, Unburden Sneasler (though that is falling off IIRC), and Samurott-Hisui is probably dead by midgame anyways.
But Will-O-Wisp is suddenly like an incredible move just because it can punish Non-Tera Fire Kingambit specifically because it needs Sucker Punch, and otherwise it really doesn't do that much else in the tier currently.
Kingambit 50/50s are not skillful and if they ever were, they stopped after people did better and better at optimizing it for Kingambit's favor. For Leftovers sets, Kingambit is gaining recovery on that amazing bulk for every turn it is "losing" a 50/50, and therefore might just live your attack anyways.
Since when has the skill we want to provide in tournaments been Sucker Punch match-ups rather than positioning around the opponent? Kingambit helps unskillful players (like me) win because if I'm losing, I can just fish some chip on the Great Tusk, and unless they have Encore Scream Tail or some shit, odds are I'm winning that game.
Some here have implied you are playing "5-6" with Kingambit and that makes it more skillful, and like, no? You could technically say that for any sweeper, but Kingambit has pretty good longevity with Leftovers and can take several attacks in the midgame.
A Life Orb Blaziken has one shot at a sweep because it will die to its own fucking recoil, a Kingambit team can use it in the midgame and then still decide to use it later when their gameplan has gone south, so they have another: Kingambit
Kingambit is already a good Pokemon without the sweeping potential, it's also just a free easy-clap wincon in the builder. You can aim to win with another plan, and still have your Plan B that is just as effective.
If people just suck, then why does Kingambit still sweep (good teams) in tournament all the time?
"It's hard to make Kingambit dominate"
It doesn't need to because unlike what you said, it doesn't need Sucker Punch to be a good Pokemon. It needs that to be able to be a second free gameplan in the midgame when you are already losing.
The fact that you can describe so much being used specifically to punish one single Pokemon should show why the Pokemon is bad for the tier.
For a playerbase that hates Covert Cloak on one single Pokemon to destroy Garganacl, we certainly are accepting a lot of otherwise sub-optimal team choices in order to check one Pokemon.
Now let's see some other cases of similarly high usage Pokemon:
-Great Tusk is already naturally checked by any half decent team, and sometimes people run lures because of the hazard metagame, not because "Great Tusk is so hard to deal with otherwise!" Preventing Spin with Leaf Storm Lead Meowscarada or Energy Ball on Glimmora, Hydro Pump on Samurott-Hisui is not an issue, and is not unhealthy, these Pokemon are meant to win the hazard metagame, and luring one of the only forms of removal makes sense.
-Landorus T in most gens mostly has few changes on Pokemon, because most teams can, again, already naturally beat it. It's not good because it can blank/sweep a game easily, it's good because it can fit on basically anything and support its team until it dies, which it is expected to generally, especially in metas like Gen 8. Sometimes some Pokemon run HP Ice to 2HKO it on Pokemon that normally wouldn't, but that isn't because otherwise Lando-T is a dominating force, it's because it can be annoying; I find this to be entirely acceptable.
-Clefable is a Pokemon that gave many headaches in various metagames, but was easy to check in most of them, it was just annoying to pivot it. Clefable had to run moves to not instantly die to any Steel-Type, rather than the contrary, and played as a Support.
By adding to the tier I hope you do not mean an insane sweeper that requires three plus checks. And if your opinion is that the metagame will bs worse because Ghosts or some shit, I made a relatively successful counter-argument in the last page of the thread.
Good day.