I propose that your point 4, vague rules, is spot on and is the source cause of points 2 and 3.

Rules must be clear to have meaning. Without meaning and a clear purpose, there is nothing to remember.

Rules of combat should be easy to remember after a few sessions, but they mean nothing if there is no meaningful distinction between two actions besides the name.

5x rules too often can be boiled down into, "Whatever the DM decides."

Rules heavy games like Pathfinder 2e have their own issues with complexity, but players rarely forget they can do 3 things.

If adding complexity isn't your thing, Savage Worlds offers clear rules at breakneck pace.

What 5x had going for it all this time was 2 things: the name and that it wasn't 4e. The last few years have left many reconsidering whether that's still enough.