The ShiftstonedEternal Power Calculator is a deck-building tool that visualizes your odds of drawing enough Influence and Power based specifically on the cards found in your deck.
I feel like you should replace Karvet. He gets a maximum of 4 cultists if you're lucky, and while the flying lifesteal is good, its stats aren't that impressive for a 6 drop. The reanimation potential with vara is there, but wouldn't Skylord Tolek or Voprex, the Great Ruin be better?
Maybe this Karvet is the way to go, but Karvet, Redeemed seems like a better choice as well.
6 cost Karvet is for sure better than any of those options you suggested. The power in Karvet is his summon ability combined with Vara’s passive. It’s similar to how azindel is so good with Vara. I will say there are other dragon slots that can be contended with, but Karvet, for sure, is not one of them.
Maybe this Karvet is the way to go, but Karvet, Redeemed seems like a better choice as well.