I don't know what you're talking about. Odyssey's level design has the depth of paper. Yea I guess it has more going on and more verticality, but it doesn't really matter much if the objectives are simple and bland, and always super easy.
3D World also has about as much variety as you could possibly ask for in a linear non-sandbox Mario game, too. I guess maybe you mean variety in movesets or presentation though, which I can understand.
One thing I really dislike about 3D World is how inconsistent its levels are thematically. Each world has its own theme, you have the water world, the ice world, the cloudy world, etc, but then it's always just the first stage that fits the theme of its world and then the other stages are just variations on other stages you found in different worlds. It kinda ruins the immersion of the game, makes it seem like nothing more than just a set of challenges for you to overcome, which itself is kind of an issue since there's pretty much zero challenge during the game's first 5 worlds and the difficulty curve is basically a flat line.
I know that Mario games aren't known for their immersion, that's not what they're supposed to be best at, but personally I really can't care about a videogame if I'm not invested in anything that's going on in it. It's just worse when you compare it to another linear platformer that came around that time, Tropical Freeze, which had masterful level design and worlds that felt entirely cohesive, with each level being part of a larger "story". Without needing to have any actual narrative.
Odyssey is a lot better at this, it's a game I could actually have some investment in. But personally, I'm never truly gonna care about Mario.