Ooh I would like to help with subdivisions. I wouldn't really no where to start for C rank and I don't know if they are necessary for D rank but here are some of my thoughts on the A tier subdivisions.
Alakazam is A- with little doubt. While he hits very hard in order to survive an attack of any caliber he has to sacrifice his power significantly. Having a random sash user is really great for stopping sweeps but with the popularity of jirachi, scizor, almost every team having a scarfer to compromise alakazam's speed, celebi and others being so powerful alakazam is not consistently one of the best performers in OU. Its bulk is pretty much nonexistent and its typing is bad as well...
Breloom belongs in A or maybe A-. While technician mach punch is really strong and bullet seed can take out a lot of threats, the popularity of pokemon that resist his STAB in OU is quite daunting. Spore might be the best move in the game so underestimating breloom is no the way to go. With BW2 being so offensive and breloom's speed being kind of crappy it is kind of hard to get him in to the field. Horrible bulk, speed, and pretty bad typing hurt breloom as an offensive pokemon but his awesome ability and spore give him a solid place in upper OU. He is good, but not that good.
Celebi probably belongs in A+ or maybe A. Celebi can handle every pokemon in the S tier to an extent, although random bug moves are a huge pain in the butt. In a rain filled metagame having a pokemon that can sponge water attacks and not be susceptible to scald burns or toxic is the key to success. Celebi also hard walls alakazam, rotom and can take hit from others like thundurus. NastyPass or MindPass Celebi is literally the scariest thing in OU right now, if a powerful special scarfer like keldeo gets a +2 at the right time it is game. Celebi can also stall things out with perish song, leech seed, and the all important recover. Celebi can singlehandedly wall many rain teams, or wall most of their common pokemon. If you want a water resist for your sand or weatherless team, celebi might be the best choice. If you want to handle keldeo, landorus, politoed, defensive politoed, and other threats at the same time celebi is hand down the best choice. Common weaknesses really suck but otherwise Celebi is a monster.
More later but if anybody suggests either kyurem for above A- I will murder you with a sharpened dildo.