I know tiers are determined by usage. What I was trying to get at was that if ditto is deemed OU (given its usage) that would effectively ban it from being used in lower tiers, correct? However, it would seem it shouldn't be banned from other tiers because it wouldn't be overpowered in lower tiers: you can't transform into Garchomp in UU, just whatever UU pokes your opponent is using, Since ditto's prowess is directly related to those pokemon, it wouldn't be overpowered in UU or NU if it wasn't in OU. Let me know if there's something I'm missing about that.
So basically, would it make sense not to determine Ditto's tier by usage (assuming it isn't put into Ubers), and instead make it effectively tier-less? It would be the opposite of putting it on a banlist.
When Umbreon became OU, it became banned from lower tiers, despite it obviously not being broken in lower tiers. What you propose is not how the tiering system works. Aside from the banlists Uber and BL, we do not base tiers on power, we base them on usage.
Now stop talking about tiers, that's not what this thread is here for.