Dragonite for B-Rank!? I don't want to live on this planet anymore.
I strongly disagree with this. Dragonite is one of the most terrifying pokemon to face in the metagame, and for good reason. Multiscale makes it incredibly difficult to OHKO and virtually guarantees a turn of set up. This is critical to it's success, because once it gets a boost it's difficult to stop it's rampage due to that invincibility facto it has with Multiscale.
Now about the more specific arguments... lets see here...
Weather: All four weathers are bad for Dragonite? Funny, I seem to recall Dragonite being an excellent choice for Rain teams for it's unique ability to spam Thunder and Hurricane at the same time.Even with a standard DD set Fire Punch will hurt Ferrothorn at +1. How is Sun bad for Dragonite? Last I checked it often ran Fire Punch, which gets boosted by Sun. Plus it resists Fire and Grass, probably the defining offensive types for Sun. Sand and Hail can neuter Multiscale (assuming it doesn't have Leftovers), but they don't really affect it much other than that. Honestly, I thought that being a bulky dragon made you GOOD against weather, not weak to it. Heck, Garchomp is pretty vulnerable to Rain teams due to his Ground type, but he's being advocated for S-Rank.
Stealth Rocks: Oh, guess we should probably bring Salamence and Kyurem-B down too. This hurts Dragonite, but the same can be said for a lot of pokemon.
Outclassed by other Dragons: Nah, not really. It's one of the best Dragon Dancers thanks to Multiscale and it's fantastic movepool. (It has priority. Seriously, not many dragons have that.) Really the only special sets used are the Rain sets, which have the unique niche of having Thunder and STAB Hurricane on the same pokemon. Also people, if you want to really exploit Dragonite's potential with Multiscale, give the SubDD set a try. It laughs at Ferrothorn and other common walls and abuses Multiscale to the fullest. Seriously, that set alone has a ton of destructive potential in a way that can't be replicated by any other pokemon.
Bottom line, keep Dragonite in A-Rank.