Your first point I don't get because I don't see how the games faked being open. They were pretty clearly on the linear side to me. And there's nothing wrong with that.
As for difficulty, I don't think it's that much different than SM64 or Sunshine. Maybe the first Galaxy was a little easier than them, but Galaxy 2 was harder. Spinning helping out with jumps didn't change that.
I dunno, they sort of felt like they were pretending to be open to me. You've got these massive planets, smaller planets, stars connecting them and stuff, but usually you just go from one to another in those launch stars, can't go backwards, don't really need to look around at all, etc. They give you space to run around but very rarely give you any reason to do anything other than just go straight to the next launch star. Launch stars themselves compartmentalize the levels in a way I am not very fond of because it means you can have a ton of level fragments without any effort to make them connected on a gameplay or even just on a graphical/spatial level. The worlds themselves contain multiple stars but don't really feel like they're the same world beyond the visual themeing and (if applicable) the world's gimmick.
Green stars in galaxy 2 were very cool though, made you look off the beaten path a little bit
Difficulty I guess I agree but I guess what bugs me more about it is often the very easy stars in SM64 are also very short. You can probably enter a level, grab a star, and get back out just in the time it takes you to exit/re-enter a course in galaxy. galaxy's levels are very long even when they are not difficult at all, which makes them feel like some boring slog that you have to get out of the way to get to more interesting courses.
Yeah you have a point with the pace. Most stars in SM64 can be collected quickly even if you're not a speedrunner. ---
Ah, yes, the Negotiator: General Kenobi <sneaky beeping>