Correct.
See this post when the SU7 Beta came out:
https://forums.flightsimulator.com/t/pre-release-testing-su7-update-public-flight/479364
So to be safe, install outside of the default (the in-game data location, not the MS Store installer).
I believe that when you joined the Beta, it only needed to download and update to the existing - so thus a smaller download. However, leaving the Beta and it’s in the default location - it will want to reinstall fully. Why it does this, I don’t know.
Sorry you have to do full install. 