LOL why is Thundurus being nominated to move down, if anything it should move up after Landorus is banned but since that hasn't happened yet that's for another time.
Anyways, so, why exactly are you guys thinking of moving it down? It has a great match-up against all playstyles and I'd go as far as to say Thundurus, OVERALL, has a better match-up against the 3 major playstyles (offense, balanced, and stall) than Landorus. Sure, Landorus is better against balance and stall (although only by a bit) but Thundurus is miles better against offense because of two major points: one, it outspeeds the crowded 108-110 speed tier and actually threatens them whereas Landorus is outsped and just dies, and secondly it has weapon in Prankster Thunder Wave to cripple the things it can't outspeed, which is huge. The sheer threat of the opposing Thundurus having Prankster Thunder Wave is enough for me to switch out any speed wincon I use, like Charizard X or Mega Gyarados. Thundurus can also choose what playstyle it wants to give hell too which is something I commonly read on the Landorus suspect thread. NP poops on balance, mixed destroys balance and stall while always retaining a good match-up against offense. Then there's the fact that Thundurus can adapt to its checks and counters, which is something I commonly read in the Greninja suspect, Landorus suspect, and that was also the reason Mega Gyarados moved back up to A+ (it has lots of coverage to adapt to whatever people are using to check it). Grass Knot Thundurus has become common to destroy Hippowdon (not even fully specially defensive can avoid the 2HKO), and you can run things like Sludge Bomb/Wave or even NP Dark Pulse/HP Flying if you want to be real. It's also not deadweight defensively because of its typing which lets it check Talonflame, Mega Pinsir, (Mega) Scizor, and Tornadus-T.
Basically, Thundurus has a good match-up against all playstyles, good emergency check to set-up sweepers, and lots of versatility to beat pretty much any check/counter it has. Because of these, I'll say to keep Thundurus in A+.