Dang it, accidentally hit the 'post' button.
The issue with a usage based tier system can be described with one Pokemon: Lapras.
Lapras in generation 6 received a fair number of buffs in the generation shift. Most notably the addition of a little egg move called Freeze Dry which is a 70bp ice type move with a tiny quirk of being able to hit water types. Now Freeze Dry was given to a fair number of Pokemon but Lapras is probably the most notable one due to it's water typing, basically giving it a pair of stab attacks that can hit everything in the game for at least neutral damage except Jynx* and Shedinja.
*using it's dry skin ability
Thankfully our good friend Aurorus is also kind enough to pass on Ancient Power to a young Lapras (it's like Aurorus instantly realized how horribe it's typing was and decided to just pass on it's few good qualities to Lapras, it's sort of like that French play, err...
cyrano de bergerac)
Now plop on an Assault Vest(I've seen people argue that assault vest on lapras is a bad idea because lapras 'isn't a sweeper' but lets be honest, when you have no means of recovery besides rest or getting hit by a water move, and your best supporting moves is
SING I don't think we're missing out on much.) and you've got a whole new ballgame.
And boy can it do some damage.Even if Lapras is essentially Rotom-W with slightly worse stats besides HP and worse typing the niche of having freeze dry and hydro pump (I prefer Surf personally, don't like having that chance to miss) means that even if it's a one trick pony in terms of what it can do that it isn't outclassed in, that is one really impressive trick.
Also I feel like Smogon, with these bans, is starting to reach the point where they ban something that happened to be among the only reliable counters to something else... like maybe this pokemon wouldn't be so threatening if you hadn't banned that one.
IDK, I think smogon is starting to become a bit of a hive mind mentality and I feel that they've begun to lose themselves in the surge of popularity they now have.