This is the result of bad writing, because Filoni is just not good at writing for live action for whatever reason. I feel like I could guarantee him covering the same material in animated episodes wouldn't have left the same feeling (nor would it have been so flabby and generally "meh").
If he'd done it right, it would have been obvious that Thrawn was several steps ahead of the game the entire way along, and that Ahsoka was getting played out. But whilst there was some amount of saying that was what was going on, what we were seeing on screen didn't look like that at all. It looked like Thrawn wasn't really ahead at all, like he barely made it out of there, and yes, only because of "DM fiat" (or "writer fiat", I guess). Filoni just couldn't let go of the idea that he needed to make Ahsoka have a big heroic moment at the end. I think he's running up against an inability to "kill his darlings" too, in that he can't even make his darlings look that bad.
Also one of the dumbest scenes I've ever seen is of the Republic letting a scary-looking shuttle land on their ship (why?!), then all lining up with guns, and carefully waiting for the guy to get out, and being like "We'll shoot you!", and the guy gets out with his helmet on (So dumb. Does he fly the ship with that on? We know he doesn't!) just to make it into a reveal when he takes it off. Just dumb bad bad dumb. On a kid/teen-oriented TV show like Clone Wars or Rebels you might forgive this, but in a full-on live action show? Absolutely brain damaged. How do they set up and perform this scene without anyone pointing out how ridiculous it was? It wasn't even dramatic because the audience knows who it is.