That’s actually exactly how the changes to matchmaking work, mentioned here :
Currently, though, any small difference, including a different class or banner, counts as being a different team. In any case, I have personally found PvP to be more diverse - and easier, tbh, as a result - than previously.
This was an interesting thread on PvP diversity, I thought, although I still think there’s room for improvement:
On a side note, I do generally agree with @Changer’s comments about using the same thing as a counter not being a good example of game balance (due to circular reasoning).