Yes the weirdness introduced by TS, especially around vuex, is really jarring. But then again, last time I tried a new medium-sized Vue project in plain old ES6, I went running back to TS, weirdnesses and all. And bit by bit, especially with the evolution of vscode, vetur, and TS itself, the weirdnesses are getting better.
I wasn't aware that vue3 was going to be written in Typescript - that is very welcome news.