Saheeli seems to work for some folks but I am not one of them. I can Oath into Griselbrand and draw seven in response to a plow which is huge.
I was, of course, a big Saheeli Oath fan when I entered the world of MTGO Vintage in late December through March. After a multi-month hiatus, though, I tried a Gush-less Saheeli Oath tonight for a few casual matches... it was not good.
Obviously, there is a lot of tweaking I can do, but I have to say that losing Gush really hurt. It's not just Mentor--although Mentor is the worst offender--all the other blue decks have much more compact threat packages. And Saheeli Oath had a more bloated threat package than regular Oath, which means it is really bloated compared to Mentor.
While I love the ability of Sun Titan to be hardcast and I find Saheeli to be a uniquely-fun planeswalker (if underpowered), it doesn't seem to be an environment where that matters.
It seems like Oath only really works as the base-blue deck that is less optimal than Mentor, but has a better Shops matchup. And if that's the case, then you have to run the tightest threat package possible since you already have the clunkiness of 4 Oath.
I've never played Griselbrand/Emrakul Oath, but I think I have to start practicing that now.
The thing about Griselbrand is that usually the worst-case scenario is that you cheat it into play, opponent goes plow/karakas/jace bounce/whatever and you draw seven cards to counteract that or to simply find a time walk and activate Oath again. You can also build your Oath deck in such a way as to enable hard casting griselbrand by making sure you run full moxen, mana crypt, sol ring, and tolarian academy. It's still tough to do, but I've cast Griselbrand quite a bit honestly. And it's funny when you hard cast gris and your opponent was banking on Fragmentize to stop your plan!
This reminds me that one of my "crazy Vintage stories" was the time that I hard cast Griselbrand... from my graveyard! Play Lotus, tap lands plus academy, crack lotus, yawgwill, replay lotus, griselbrand. GGs.