That's completely missing the point. Funbro is beatable too. Every argument used to defend revivecats can be used to defend funbro. But at least funbro actually exists in the real game. Revivecats is 100% fanficshit. It's 100% speculation. Assist was removed in the same generation Revival Blessing was implemented. Even if the two moves existed in the same generation, there is no way in hell Gamefreak would allow Assist to select Revival Blessing. Anything Goes is supposed to be like the normal cartridge with absolutely no restrictions. Not fundamentally changing the game's mechanics because "lol revival blessing calling assist would be funny XD"It's not going to be banned, being uncompetitive or broken is completely irrelevant since this is Natdex AG, where No Guard Fissure Machamp is legal.
I would suggest including 1 or 2 members with Extremespeed (Arceus/Mega Ray/Zygarde/Deoxys etc) as counterplay to Prankster Assist. Its annoying but far from unbeatable.
Assist calling Revival Blessing is utterly absurd and should not remain. It would NEVER happen in the game. Its just as ridiculous fanfic bullshit as letting Slaking get Huge Power in AG because "LOL ANYTHING GOES". Fundamentally altering the mechanics of a move based on pure speculation, (and unfounded speculation at that) is frankly stupid.