UU has been in a very interesting place this month ever since Darm and Torkoal dropped, and I won't lie, this whole discussion on the problem of Sun in UU has been incredibly polarized. I've noticed a lot of people cite abusers as the issue, and others saying that setters are the issue. It's indisputable that there is a problem with sun itself, though, and I don't think anybody is here to debate that.
It's hard to pinpoint the exact issue, because Sun in its own right wasn't broken until Darm dropped, but the abusers don't work to nearly the same effectiveness without it. Something I learned is that metagame trends are usually what define what we consider broken in a tier. The metagame is ripe for Venusaur/Darm's picking, with many top threats being utterly dismantled by their STABs and offensive options as a whole, but the thing is that this wasn't exactly a problem until Darm and Torkoal actually dropped. It's extremely easy to slap on a Torkoal, Venusaur, Darmanitan, maybe Ninetales, and two filler Pokemon, because the sheer strength that comes from having that base core is really all you need. It's extremely powerful, and despite how cookie cutter it is, whether you can predict it or not, it's going to be a massacre regardless. I believe the best way to describe this issue is that
sun has way too many effective, overwhelming options, be them nuclear or utilitarian.
So, to parse the problem, I believe the best way to look at it is to consider what exactly creates the strength of these options. The obvious answer right out the gate is Sun, but the thing is that the weather on its own is not a problem, as proven by metagame trends prior to Darmanitan's drop. The playstyle by its base is not an issue, and outright banning it, I feel, is a step that's a bit too far. Instead, I want to look at the combination of options themselves in Sun.
Venusaur + Chlorophyll Abusers
Venusaur, out of all of them, is by far the best Chlorophyll abuser. Incredible dual STABs, Growth as a boosting move, and new, extremely powerful tools in Weather Ball + Earth Power give Venusaur arguably the best, most effective coverage in the entirety of the tier (and maybe even the generation). I feel Venusaur has a similar issue to Gyarados where you have to rely on mindgames in order to survive its onslaught before Sun expires, which, given how its coverage is insanely strong, is a very problematic "check" of sorts, as prediction being the best way you beat something is never a good sign of a healthy Pokemon. For the most part, I actually completely understand the decision to suspect Venusaur first as opposed to suspecting Sun itself or Darm.
However, I rarely see people discuss the effectiveness of Chlorophyll abusers in general, and in here lies the problem of hunting down Venusaur specifically. Things like Vileplume and Shiftry, while less effective in a vaccuum, still yield incredibly powerful offensive options that, in some cases, can be even more effective than Venusaur. Vileplume has access to Moonblast--which is a great option against Noivern--as well as the same dual STABs as Venusaur, and Shiftry has access to Dark STAB and is a great check against Doublade, which can usually Shadow Sneak a weakened Venusaur. While these two examples aren't as immediately dangerous as Venusaur, I want to highlight the exact reason why this would still be a problem.
Darmanitan.
Darmanitan
I don't need to show you the absolutely asinine calcs that this behemoth rocks for you to know that Darmanitan is an absolute powerhouse in Sun. However, what I don't see people often talking about are its other moveslots. While Flare Blitz in Sun with Sheer Force and base 140 Attack is not even remotely a switch-in, the fact that this thing has Trick, U-Turn, Earthquake, and Rock Slide as options as well is an absolutely horrifying prospect. It has a similar issue to Venusaur and co. regarding its switch-ins, however, I believe that even in Sun, its options can be punished, especially with the newly dropped Rotom-Wash and the rise of defensive behemoths such as Rhyperior.
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The reason I bring these two in accounting for is because of something that I seldom see talked about: their incredible synergy. There's a reason the cookie cutter sun core has become so powerful in the tier, and it's because it's legitimately an amazing offensive core. The options these two components of sun have to support each other is absolutely mind breaking, and I believe this is the problem of sun.
Darmanitan pries apart any potential Chlorophyll check, and vice versa with Darmanitan. These two together lack switchins and cover one another's back in the process, which is why they work so incredibly well together even if you can expect to see it. Suspecting Venusaur is definitely a good step, but, that doesn't change the amazing synergy Chlorophyll abusers and Darm have in the tier. Once Venusaur is banned, new Chlorophyll users will rise to take its place, which, in combination with Darmanitan, would yield the same exact problem, even with Venusaur being gone.
Ideally, we want as little bans as possible and for the metagame to have as many options as we can give it. So, I have two potential ideas if Sun proves to be too strong even without Venusaur.
1: We suspect
Chlorophyll + Drought
This is taking some inspiration from Gen 5's Drizzle + Swift Swim ban, but I believe given my observations, if we wanted to stop the reign of Venusaur specifically, I think the approach would be to suspect this particular combo. Though, given Venusaur's upcoming suspect, this very well could be the only thing we need to do. We can't entirely ensure that this combo is the problem or if it's just Venusaur itself, so I think the council's voting on a Venusaur suspect is a good move to minimize potential bans.
2: We suspect
Darmanitan
This one I'm less as sure about, because Darmanitan faces many more immediate issues unlike Venusaur/Chlorophyll. This mainly comes in the form of recoil damage, a hazard weakness, and a priority weakness. It can wear down very easily even with its groundbreaking power, and pretty much necessitates a choice item to retain consistent effectiveness as a breaker. I've seen the stray HDB, but this set is picked apart easily by Pokemon that are faster than it--which aren't far and none--due to the loss of speed. Without Darm, Chlorophyll retains its gargantuan strength but is somewhat gimped by the breaking power that Darm provides for Sun that allows for abusers to easily clean in the lategame. We can refer to pre-April drop trends for the validity of this idea.
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Personally, though, I think the idea of suspecting Venusaur is a great first step to figuring out sun for now. Darmanitan is not as consistent as the Chlorophyll abusers despite its strength and breaking power, and it has a lot more immediate answers as opposed to stalling out sun so you don't get obliterated by Chlorophyll abusers. If sun proves to be too strong even without Venusaur, I personally think Chlorophyll + Drought might be the next good step given how Darmanitan on its own hasn't exactly proven as much of a problem.