Phil Lord and Chris Miller, for example, probably could tell people what their vision for Solo: A Star Wars Story would have looked like, but it appears that Ron Howard did the bulk of the filming, leading to that film’s theatrical release.
More often than not, the filmmakers were released early (or earlier) in the process, and didn’t produce enough footage to complete their Cut.
Other films that position themselves as unfinished made compromises during the production cycle, but that’s not to say they’ve earned the right to go back and release a reassembled cut of their original footage.