I don't see Stewart replacing Beleskey at all. He doesn't have remotely the same type of shot, and doesn't provide remotely the level of physicality and hitting that Beleskey did. I also don't think that a 15 goal guy replaces a 22 goal guy, unless you're also willing to say that an 8 goal guy rep,aces a 15 goal guy. (It's irrelevant what people think Beleskey will do this year, that's what he DID last year). I really think people are understating Beleskey's physical impact and grossly overestimating what Stratton brings in that department on a game to game basis.
The whole "he out scores Beleskey" thing is also misleading (assuming he's the third line guy), unless you're convinced he will be racking up assists on the PP or convinced that Rakell and/or Sekac will develop shots. You can't give out three assists and score, someone has to be able to actually get it past the goalie to get an assist.
He's not a bad pickup, but he's hardly the missing piece.
As much as I like Bels, I dont think he ever hits 20 goals again. Offensively Stewart is just better, definitely more talented. Put on a line with a little playmaking, and defensively responsible, he should be a good fit. That being said I think Bels' energy and compete level make him a better player overall. All in all I'll take Stewie for a 1.75 show me contract over Bels' UFA cashing in contract.