I should preface this by saying I'm only mid-range in terms of PVP skill at the moment, however I believe it is still reasonable for me to point out that Maycasts of any kind, especially Pet Maycasts, add a disproportionate amount of randomness and anti-skill to a meta that is already far too luck-based as it is.
Every move that a player makes should be more or less their decision, not decided by external RNG factors. There is already a substantial amount of randomness in the game in the form of deck draws, accuracy, pip chance, and shadow rating.
Some amount of randomness is acceptable, and even fun. Too much randomness is bad and causes players to feel frustrated and helpless. This is the underlying reason for why Critical was reworked, and I see no reason not to extend it to Maycasts in general.
I understand that many have spent time developing their Maycast pets or attaining Crowns gear that may happen to have Maycasts added on, which oftentimes have additional stats that are worth having even without the Maycasts themselves.
So I suggest that for instances like these, that only the Maycast stat portions of these items and pets be disabled for PVP, while allowing the rest of the stats of the item (and the item itself) to remain and be usable for PVP, minus that Maycast.
As an example, a May Cast wand attack would instead become a static item card in your deck, that you would have to choose to cast, instead of hoping that RNG casts it for you.
A May Cast Fortify pet would instead come with a few Fortify item cards (for use in PVP mode only), and would revert back to normal for PVE.