I like all of your adds, except I'm not sure what you're trying to do with Leonin Arbiter. Is he there to hose fetchlands? Tutors? Either way, I found he was a pretty ineffectual hatebear back in the Standard days, even when you could pack four of them. Some people on this forum have tried Aven Mindcensor for a similar effect, though I don't know of its success rate.
Kor Sanctifiers might be a necessary evil, as I think you want a few Disenchant effects in white, outside of universal catch-alls like Oblivion Ring. Lightning Strike is a fine cut, because you're already running two functionally identical cards. With so few cheap creatures in blue, I think you might be better off cutting another blue four drop for Venser, and Dungeon Geists seems like the weakest link. That, or Crystal Shard, though it may work better in your environment if you push midrange.
I might just have been blinded by the Death and Taxes resurgence. I planned to put it in for testing, but you're right, it might be disappointing. I agree with the Sanctifiers principle, but I just found that it is quite unwieldy and rarely gets played. The kicker makes it unattractive for tricks, and the double white is often a concern. Also, people in my playgroup rarely bother with sideboarding, so these cards just see less play (though I still insist on maintaining quite a few of them, e.g., Disenchant itself is still in there). If we suppose that Leonin Arbiter disappoints, would you rather see Mana Tithe or Spear leave over Sanctifiers?