Dragonite's bulk is pretty situational, depending solely on mulitscales intactness. Since stealth rock is ever present that bulk will always hindered. I think it's fine in A.I would like to nominate Dragonite for A+ because of its sheer unpredictability, which it can use with its very diverse movepool to eliminate many pokemon that switch in to it. It can use Thunder Punch (or Thunderbolt depending on its set) to beat Azumarill, Gyarados-Mega, Togekiss, and Skarmory. It can also take hits very well due to Multiscale, making it extremely hard to OHKO without Stealth Rock. Access to Roost lets it temporarily have only a 2x weakness to Ice, and allows it to take hits after its Multiscale is broken! These calcs explain how strong Dragonite is.
252 Attack Life Orb Mamoswine Icicle Crash Vs 0 HP 252 Defence Multiscale Dragonite: 268-320 (82.9-99%) Guarenteed 2HKO. Just out of reach.
+2 (weakness policy) 252 Attack Dragonite Waterfall Vs 0 HP 0 Defence Mamoswine: 430-506 (119.7-140.9%) Guarenteed OHKO.
252 SpA Choice Specs Greninja Ice Beam vs 0HP 252 SpD Careful Dragonite: 270-320 (83.5-99%) Guarenteed 2HKO. Not even greninja can do it!
+2 252 Attack Dragonite Dragon Claw vs 4HP 0Def Greninja: 372-438 (130-153.1%) Guarenteed OHKO.
Not even Modest+Choice Specs Greninja succeeds against max HP max SpD Dragonite!
252 SpA Choice Specs Modest Greninja Ice Beam vs 252 HP 252 SpD Careful Dragonite: 296-350 (76.6-90.6%) Guarenteed 2HKO.