not really, Protean Mew would definitely be manageable in Ubers considering it's not that bulky for Ubers standards and also has even lower Special Attack than Greninja which isn't even viable as an attacker in Ubers. Ubers allows things like Primal Groudon and Geomancy Xerneas, and Protean Mew is basically nothing compared to them it'd be too much for OU to handle though, yeah