So, I've not played Vintage in a while. Mostly because of real-life concerns (toddlers and work take up amazing amounts of time), but I have retained interest in the format, and been reading up things that have been happening. I have a few thoughts:
I think Mentor is worse than Tinker. Some people keep saying Mentor is "only" a 2/2 creature for 3. It's not. Mentor is two Storm spells that keep storming after being cast. For three mana. With a free 2/2 body attached.
The only finisher that even resembles that kind of power is Mind's Desire, and that costs 6(!) mana without a free body, and only keeps going during the same turn, if you're lucky, and it's unrestricted. I don't see anyone arguing Desire is safe for unrestriction.
I don't know enough about Gush to have a valid opinion on the matter, but (correct me if I'm wrong), Gush was played in pretty much all blue decks prior to its restriction, correct? Post-restriction, the only Blue deck that remained viable was Mentor. That, to me, says two things:
A) Gush was unarguably the best blue draw engine - everyone used it (reducing deckbuilding choices, although not necessarily strategic diversity). Hence, IMO, it was a viable target for restriction (but not for the reason given), but since it did allow a variety of strategies to abuse it, it was not a necessary target. Brainstorm was much the same, and was allowed in the format for much longer. Again, I'm no Gush expert, and whether the ubiquitous card in question was Gush, Brainstorm, or whatever, doesn't really matter.
B) Post-restriction of Gush, only Mentor remained as a viable Blue deck, because of 1) the density of 0-1 mana restricted card drawing/filtering spells combined with 2) Mentor is busted.
From B), there are three possibilities (I think). One, Mentor is a fair target for restriction - it's broken. However, I don't think this will end Workshop's dominance. I may be wrong there. It's possible Mentor decks are too good against the decks that beat Workshop, and that with Mentor gone, those decks will once again have free(er) range to feed on it. It's also possible that with Mentor, the one thing that kept at least a deck in the fight gone, Workshops will simply reign supreme, and that part of the problem will have to be addressed some other way.
A third possibility is that a critical mass of restricted draw spells has been reached, Mentor is only a symptom and the blue tempo decks will simply switch to the next best threat and keep dominating the Blue part of the metagame without significantly shaking up the rest of it. I don't think this is the case.
IF it is, though, short of outright banning some cards (against the point of Vintage, IMO), or banning specific card combinations, maybe there should simply be a restriction on how many restricted cards a deck can play?
OK, enough rambling. If you've made it through all that, kudo's.