It's weird, the Warriors are basically in the same position with respect to centers as the Celtics are (or will be starting this Summer when they care about wins), so I should in theory love the idea of adding Capela, a young, highly efficient, and battled-tested true C... and yet, I don't.
I like Chriss, Looney, Spellman, and Smailagic for I think the roughly same reasons you guys like Theis — undersized but skilled and hard-nosed bigs whom I've grown attached to as "my guys." And I don't really like Capela, for no good reason other than the fact that he's a Rocket (plus not super charismatic-seeming, at least not in terms of his on court presence). And as talented as he is, I think he's at least partially a Harden creation.
I'm sure there are plenty of teams out there who would happily take Capela off their hands, though. 25 y.o. bigs capable of putting up 18 pts 15 reb 2 blk per 36 on .650 ts, and who have gone toe-to-toe with Rudy Gobert in the playoffs and vanquished him, do not grow on trees.