I don't understand your logic in saying that the card is inefficient against mentor because it "costs more than the cards it's answering." if you are using supreme verdict to deal with 1 mentor then it's using it inefficiently but when it's mentor and tokens given that each token adds to the cost of the mentor it is an uncounterable board wipe that happens to be pretty good. Also the gush engine is only good if the gush resolves, standstill decks play considerably more counter magic than mentor so yes if the gush draw engine is uninterrupted then mentor is advantaged but that can be said of any deck that goes uninteracted with. Standstill doesn't have to win with factories, Jace is also a viable win con in the deck. Moat is a beater in most match ups right now. Shops, dredge, mentor, Tinker blightsteel, all cannot beat a moat.
Four mana, three of it colored, is a lot more than
, especially when Mentor can kill you in that one turn window before you can Verdict. The tokens are generated as a byproduct of casting other spells and so there isn't really a tempo disadvantage - the Mentor pilot is still drawing cards, filtering, Delving and progressing their game plan. A Verdict that wipes the Monks doesn't undo this and it's easy and frequent to follow up with another Mentor that can't be answered. That's assuming the Landstill player is able to find one of their two or three Verdicts given the short clock a resolved Mentor represents. Fighting Gush and the other draw spells is not easy to do - Spell Pierce and Flusterstorm normally don't work which mean you are relying on Mana Drains and Force of Wills. The cantrips and manabase keep the gas coming and you are generally better spent saving your counterspells for the Mentor itself, Cruise/Dig, and Dack/Jace.
I beat Landstill three times in splitting a Black Lotus/Ancestral Recall with Brian Kelly at EE3. I've played against the VSL UW version three times recently in online dailies. In these 6 matches, I think I lost 1 game. My overall impression of the match up is that it is highly favorable for a competent Mentor pilot...perhaps 75-25 or higher, not even close to a coin flip (respectfully disagree with you here Josh).
Moat is an interesting idea but it is certainly has not been a part of recent lists. I normally keep 1-2 Wear/Tears in the deck as they kill Factories and Crucibles while being instants to pop a Standstill at EoT. Against the Moat control decks that occasionally pop up, my strategy is generally to commit one Mentor to the board and then use card filtering and Probe to force an EoT Tear through. That or ultimating a JVP has won me a couple of games here and there.
