i have an idea that could help make more accurate tier lists,
come next tiering update, move pokemon that have megas down a tier, like say, regular mawile would become uu, but mawilite would still be ou, and banette would be nu, but bannetteite would still be ru. we don't know how much potential a pokemon has without it's mega until we can separate it from it's mega form. mega kangaskhan is ubers, but regular kangaskhan has fallen to nu because it is nowhere near as good. if some pokemon were too strong, they would be moved back up, but some will fall down further
perhaps, for balance, this wouldn't be used for pokemon that are already good without their megas, like scizor and tyranitar, but i really don't like that mawile's unique typing and pretty good abilities can't be used without the sheer power that huge power forces mawile into ou even without it's mega.
It's important to look at the tiering system the correct way. There are four actual tiers, OU, UU, RU, and NU. Pokemon are distributed to each of these tiers based on their usage; if a pokemon doesn't get used enough in OU, for example, it drops to UU.
Each tier also has its own ban list. UU has BL, RU has BL2, and NU has BL3. OU has Ubers. So if a pokemon is in one of the four main tiers, but is suspected and the community decides it is too broken for that tier, it doesn't move up or down a tier, it just goes into that tier's ban list.
Items are not classified based on usage but are either suspected and banned from a tier, or not. They don't affect the placement of the pokemon in one of the four main tiers any more than the existence of Leftovers or Life Orb would. The fact that a pokemon can become OP because it can hold, say, a life orb, could send that pokemon to its tier's ban list, but the item's existence alone would not change the pokemon's tier except that the fact that it makes the pokemon more useful could mean that more people use the pokemon more often. We certainly wouldn't ban life orb in that instance, because every pokemon can take advantage of it and it's just this one pokemon that's broken.
A mega stone, however, is pokemon-specific. So, because in the case of Gengar, Lucario, and Kangaskhan, it was the mega stone itself that was the problem rather than the entire pokemon, it was thought a better idea to simply suspect the stone itself, kind of like Soul Dew was suspected rather than Lati@s (though Latios was Uber for a while in Gen IV iirc, but not just because of Soul Dew). As the eon twins were the only pokemon that could utilize Soul Dew, instead of banning both entire pokemon, just the item was banned. Because Lati@s were still very viable even without Soul Dew, people kept using them and so they stayed in OU.
So that's the logic behind the system. Pokemon won't be arbitrarily moved up or down a tier because Mega Stones don't sit in any particular tier; they either are or aren't banned from the tier the pokemon that can use them is in, which is based on that pokemon's usage. We can say that Mawile is in OU *because* it can take advantage of its Mega Stone so everyone uses it, and Kangaskhan is in NU because it can't so nobody uses it (outside of NU, of course).
