Comparing Mario 3D World to Mario Galaxy is not super wise, imo. I mean, yeah, they're in the same franchise, but they have completely different target goals in mind. Whereas Galaxy was a Mario adventure similar to what Mario 64 had to offer, with 3D World they tried to tackle the multiplayer aspect of NSMB Wii and make it a fun, chaotic, multiplayer experience. They are 100% different games save for the fact that they have "Mario" in the title.
I would definitely like a Mario game that followed in the footsteps of Galaxy because I like big 3D worlds to explore, but I don't think 3D World was a downgrade. It was more like a sidegrade, tbh. They're always exploring new things with Nintendo games, and 3D World wasn't the exception with the 3D multiplayer aspect. Plus, the level design in 3DW is flawless. It has some of the best platformer levels Nintendo's ever done.