Doesn't KMP assume your team is comfortable working in Kotlin?

Yes, that's fair. I'd argue, though, that the training required to get your team up and running should be fairly minimal - Kotlin is a very easy language to pick up, especially for people coming from TS - and will pay off dividends in the medium to long term.

Well, it assumes the model is.

KMP can be seen as a token optimization at this point. Business logic is shared and doesn't have to be rewritten in Swift.