I've got 2K CR on Mew.
I feel like players won't want to deviate from their current strategies to incorporate more fire power, as that fire power could end up moving enemies around via uncontrollable knockback, or otherwise. Mew's abilities seem to offer some kind of protection, either as stats, or status resists, or heals, or something... but whatever it is, Spiral Knights was not made to have healing on the part of the knight. Likewise, Bulbasaur's poisonous nonsense is likely to fail due to poison's largest strong point being fighting off healers by turning them to KILL THEIR CHILDREN, the gremlin knockers. This works on something like venom veilor, where the poison is constant and controlled, but on something with a lengthy recharge rate, there would be no point.
What would you say? I mean, it'll all come down to the implementation and specifics, but speculation is fun in its own right.
OP is in the eyes of the beholder, therefor I will not bet. We'll most likely see players calling all pets (especially in LD) OP repeatedly and they'll become the next hammers/polarises.
958945084935743857348573408 CE ON ALL PETS!
EDIT: Just saw [the most]. My argument still stands though, but I do believe the mew will be the most OP. Healing/buffing players that can already easily heal/buff themselves with gear? Um, no thanks.