Every time I post my 3D World move set exhibition video this person leaves very sad comments:
They remind me of Spieler Eins or Freezie KO from the old site.
That's an oversimplification. Some of the green stars are like star coins, yes, but some are sandbox-esque challenges like catching rabbits, rescuing Captain Toad, and stuff. We were talking about comparing it to Galaxy, so I was including other things like collect 5 key coins to open the path, which is like collecting launch star fragments (which was specifically mentioned in the post I was quoting as something that makes Galaxy feel more sandboxy, and such. There are a few levels where the whole level is exploring a large area or multiple areas to find key coins.
As for 64, a lot of levels in 64 have the problem where multiple stars could have been obtained on the way to another star but the game kicks you out of the level and makes you do the whole thing over again just cuz. For example here's every star in Bob-omb Battlefield:
The first star is basically a flagpole, and the second star is doing it again but faster than Koopa the Quick. The chain chomp star is on the way and there's no reason you shouldn't be able to get it on the way to the top of the mountain. All of these stars are challenges you will find in 3D World levels.
Tall Tall Mountain, as you pointed out, is especially egregious in this regard.
Odyssey thankfully fixed this.