Spent enough playing this meta that I wanted to add some personal thoughts and some noms of my own
If it wasn't unwallable with Specs alone, Tera Fire and sun tip it way over the edge. Throw Nasty Plot, Wisp, and Tera Grass into the mix and it can just wear down or shred through the chosen few that can stomach its STABs. Way too much guesswork goes into trying to deal with it, and its checks generally have no reliable recovery or are very passive or niche. To top it off it's great against offense with a Speed tier way too good for a breaker of its caliber, huge resistances to Sucker Punch and Gholdengo's STABs, and the option of Scarf. Versatile, reliable, unpredictable, meta warping and defining. Best mon in the tier, and there's hopefully a ban coming its way soon to show for it.
Everyone who's gone against this thing knows the deal. So, so hard to deal with. The fact that you generally have to go about dealing with Rest Ape and Taunt Ape in different ways makes it very tough to rein in if it gets going and you guess wrong (or even if you guess right most of the time). Same deal with the different Tera types it can choose from. Warps the meta by invalidating slow teams and pivoting playstyles that feed Rage Fist and forces them to either scramble for niche answers or just lose to it.
Much more individually potent than the rest of A+ (barring Ape). You could argue Valiant, but that's easier to check as a whole because mons that resist its STABs are in decent supply and it's easier to revenge kill than the dog, barring relatively weak Booster Energy sets. What really makes Chien-Pao stand out for me is that it poses such an immediate threat in a metagame where many of the top HO mons rely on extensive setup. Being one of, if not the best revenge killer and general anti-offense mon in the tier helps its case just as much. Add in that it can break its own checks down with insanely strong Tera STABs and it's hard to argue that Chien-Pao isn't a top 5-6 mon in the current meta.
Probably the hardest mon in the tier to consistently take down, and the best defensive Tera mon in the tier. Tera Fairy alone blanks every Dragon in the tier, most Chien-Pao, and Annihilape, which just about nothing else out there can do, and Tera Water and Poison have similarly impressive résumés. Recover and the status immunity are insanely valuable, and Salt Cure hugely complements its longevity by making it seriously difficult to switch into and forcing progress against every playstyle. In addition, it can be a wincon with ID+Body Press or Block, or it can experiment with coverage like EQ and Heavy Slam, and all these traits together allow it to pivot into and 1v1 almost anything it wants. Oh, and they went overboard making this thing immune to Tspikes. I know I'm saying a lot that's been said already, but this absolute behemoth carried my reqs run and I've been called dishonest more than once for using it as much as I do. Crazy accusations, I know. Bottom line, Garganacl is truly phenomenal and deserves to rise to A+.
Underrated and underutilized force in this tier. Gholdengo or not, Spore is still unbelievably valuable. Mach Punch gives it serious utility against the various Dark-types in the meta, and Sash sets can get off a free Spore or a valuable hit against an Iron Valiant or Espathra that thinks it's about to run away with the game. Tera Fire, in my opinion the best set, frees Breloom up tremendously by dispatching the Spore absorbers, and its other new toys in CC, Gunk, and Bulldoze leave no bulletproof checks and open up options such as Band to wreak havoc on bulky teams. It helps that Breloom has a naturally solid matchup against much of the defensive meta, most importantly Ting-Lu. Not the easiest threat to build around, but so rewarding when utilized correctly that I believe it warrants a rise to A-.
-> B (at least B-)
Kudos to Ceruledge, not many mons like it survive the "new toy syndrome" phase. It found a new lease on life with those defensive Tera Flash Fire sets, it provides a lot more utility than expected and can send a lot of offensive builds packing if it gets a good chance to set up. Beating Great Tusk with Bulk Up is a huge draw, as is outspeeding Gholdengo. A decently strong Shadow Sneak is always good to have as well. Still struggles to make headway against defensive teams, but it's taken on a niche as a credible offensive threat worthy of a rise to the B ranks.
-> C+ or B-
Dracovish on a budget. Rain's resident sweeper for the moment. The sheer power of Tera Water Wave Crash gives it a sufficient edge over Barraskewda, since the ability to just click one move and drop resists is absolutely invaluable for a rain team.
-> C or C+
Has an interesting niche with a very difficult to block Volt Switch. STAB Earth Power and Tera Ice are huge assets that pick apart common Ground-types, and because of Sandy Shocks's good SpAtk it hits most targets fairly hard. A great Speed tier is what really sets it apart from Rotom-W, outspeeding threats like Chi-Yu, Gholdengo, and Baxcalibur that Rotom-W usually falls short of. Also has the option of Stealth Rock.
Great mon, lots of lategame potential with Supreme Overlord. Its ability can limit it, though, because preserving Kingambit's bulk to force it into a do-or-die situation late in the game takes away from the tank role it may need to fulfill earlier on. In addition, by the time Kingambit can get a significant boost from Supreme Overlord, a teammate may have already Terastallized, so it may not be able to use the defensive Tera that would allow it to set up against and beat a check such as Great Tusk. The meta's unkindness to Sucker Punch users is most problematic, with various fast Dark- and Fighting-types being among the best Pokemon in the tier and techs such as Tera Fighting Gholdengo and Tera Fairy or Will-O-Wisp Dragapult being possibilities as well. Kingambit just doesn't quite have the consistency or the overall potency to be worthy of A+.
Rapid Spin users are so important in this meta, and I can see where Iron Treads fits in as a fast, Gholdengo-smacking alternative to Great Tusk. Knock Off and Volt Switch are both amazing to have. The main problem with Iron Treads is that it doesn't really defensively answer many offensive staples other than Espathra in practice - the Dark neutrality and Ground and Fighting weaknesses pose huge problems for it, and together with its lesser offensive presence, it's just usually outclassed by Great Tusk.
Hand in hand with the Floatzel rise. Despite better coverage and Speed, it just can't match Floatzel in terms of damage output, so it finds itself just barely outclassed right now.
Really only checks one or two good Pokemon that have ample ways around it. Not the offensive behemoth it used to be with Choice Band either, stuck in a meta with more dominant Rock-resistant Pokemon than ever before, especially Great Tusk. Gonna be a tough generation for the king.
Also agree with these noms: