I don't disagree, but I don't entirely agree either. I think there was a lot of potential that got watered down. Kai's heel turn in the third act came out of nowhere, and his reasoning was weak at best. Olaf adds nothing of value at any point, and quite often seems to be added in as an afterthought, like the visual version of ADR. The trolls have excessive screen time, and the pointless fixer upper song.

I'd make some small changes to make Frozen, in my opinion, way better. First, Kai doesn't heel turn. He just admits, more pitifully than antagonistically, that he wasn't in love, and that he just wanted to salvage some kind of position for himself as the seventh son. "I like you. We have so much in common, and we get along so well. I want to love you, and maybe someday I will, but love isn't what I want right now." Now he can be reviled and/or pitied, depending on how you feel about such things. He still imprisons Elsa, but it's for honest reasons. He sees her as a threat, but also as Anna's sister. He won't kill her, but she has to be stopped for the good of the realm that Anna put him in charge of before she was hurt. This, all by itself, would make the story far more compelling.

Aside from that, be rid of the visual noise that Olaf represents, and the fluff added to the trolls to make them more merchandisable. The rest is pretty compelling all on its own, from my perspective.