It was hard not to think about Caissie every time Evan Carter came up to the plate this October. For the past two years any time I've looked at Caissies performance in the context of his age Carter was the only guy ahead.
Caissie looks like about as safe a bet to be an impact hitter as there is, not just in the org but in the minors. You mention 70 grade power, but it might be 80 grade by maturity. He hit, IIRC, 117 MPH last season. Only 26 guys have crossed that line in the last three years. And at 20 years old that aspect of his game should be improving still. The patience too looks pretty elite.
Tbe contact draws a lot of hand-wringing, but I think those concerns are overstated. We don't have full plate discipline numbers for the minor leagues, so people have to settle for K rate. But K-rate =/= contact rate. A guy running an elite walk rate is going to inherently be in a lot of deep counts, which will lead to a lot of Ks. We do have swinging strike rate for MiLB, and Caissie was 35th out of 64 guys in the Southern League this year. Caissie is not a Joey Gallo or Patrick Wisdom level contact bat. He's more Kyle Schwarber, who has bad but not awful contact rates but runs huge K numbers dye to walks.
Schwarber is the cautionary tale for Caissie though. He had only occasionally been an elite bat, and as a bottom of the defensive spectrum guy you need an elite bat to exceed the 2.5 WAR neighborhood. I'd expect Caissie to provide more defense than Schwarber, though not a ton. But there's pressure on the bat to be like a 130 wRC+ or better for him to be an impact player. That's a tall order for any minor league hitter, and so like several others in the system even though I like him a ton if we need to move him so be it.