I don’t necessarily think nerfs are the answer, or introducing new power creep monsters to counter them. Buffing old monsters will work just as well to achieve it.
But I do think,that variety is important, especially for the top ranks, to keep players interested in the game. If there was one team to beat all other teams in PVP, because it was the “best”, then PVP would become a “who owns the most monsters wins”, which would be incredibly boring. Ziberius opening… motor at 5, autopoison and GT endgame… or something like that.
Battles would become identical and incredibly boring at the top ranks, and lower ranks wouldn’t have any way to enter the top beyond spending more and getting the right monsters.
Instead, I’d love it so that every monster had a counter that was relatively useful, rather than each monster being a definite include (like Aegis was pre assassinate). Completely understand that this is near impossible to achieve with balance in the game, but would be nice
Devs have definitely made steps in the right direction, e.g. introducing assassinate to counter the oppressive aegis, bane for sleeplocks, leo for the stun stacking, nerfing chrono and deathgazer, etc, and I hope it continues that way.
I agree that right now, there’s no one team to win every battle, but if someone owns one of those monsters, 95% of the time they will be used in their team for PVP, and if someone owns all of them, they will probably win 95% of battles.
It would be good to see some counters to these - if not nerfs, or new mons, buffing existing old monsters could definitely work to achieve this 
But this is all just my personal opinion - everyone else may disagree 
TL: DR - Jain thinks Variety > One team to rule them all