Well, I also suggested he might be worse too but you chose not to quote that part for some reason.
If you really want to know how I think about this subject you should have stayed with the last part: "likely, he would be about the same anywhere".
You are acting as if Poeltl had somehow improved his game dramatically and that couldn't be further from the truth. He's pretty much the same player he was when he entered the league only with more minutes, more experience and more confidence.
If you told me Poeltl had developed a jumper, or a post up game, or did anything much different than what he used to do then I might be on board with the idea that the Spurs really did something special to develop this guy (like they did with Kawhi's jumper). But as things are I can't claim that because Poeltl isn't showing us anything that he didn't already show in Toronto. If anything, the biggest change, game wise, is the fact that he's now a much worse FT shooter.