Capela is a better matchup when we're playing Philly. Indy maybe. But not many other teams.
The things Capela does well, rim protection and rebounding, maybe replaces the things Theis does better than him? I don't know. Capela can't shoot, can't be trusted with the ball at the end of the game because he's an awful FT shooter, and has no real post up game. He's basically a more accomplished version of what we hope RW will become.
Theis can at least keep a big honest with his 3 pt shooting, isn't useless in P&R, and for all Capela's shotblocking chops, he's less than Theis on a /36 basis.
I don't know, maybe Danny loves his contract and the value a mid-level deal like his can bring if Ainge needs ammo for a big trade down the line. But does this make us a demonstrably better team the rest of this year? I don't think so. If it does, it's marginally better, at best. I would pass on this deal, I don't think Capela fits our team.