@Tom-Bombadil You're talking about restricting 4 cards instead of restricting just 1 (Mentor). I don't see how that's better. I also don't believe restricting Gush stops Mentor - but restricting Mentor makes Gush less oppressive.
It really hurts to hear that "Mentor dies to removal". That's not understanding how Mentor works AT ALL. You can easily play a Mentor and generate 2 tokens immediately with it and not care about spot removal. If trading 1-for-1 with removal (tapping out for Mentor without phyrexian mana or moxen) is a common play in Vintage is just because you have 4 Mentor therefore you have the possibility to gamble on your opponent not having removal. If people only had 1 Mentor in their decks, I HIGHLY DOUBT playing Mentor turn 3 without any other spell would be a common play.
Also, if you're playing sorcery speed mass removal to deal with Mentor, you're limiting yourself a lot. Terminus is only good in Legacy because they have Brainstorm. If you're playing bad mass removal like Radiant Flames or Supreme Verdict, I'm really fine with it: if it resolves it's still 1x1 in terms of "pure card advantage" (but you had to pay 3-4 mana for it); and I get to play with 4 Mentor. If you shove 4 mass removal spells in your deck, then well... me winning with Mentor or even a PW is just a matter of outplaying those 4 suboptimal slots.