I mean, no one is denying that one game is more exploration heavy. Just that your assertion is, subjectively, wrong to me. I don't think either game is particularly great at having hidden content that's inherently interesting to find, to be honest. It's all an excuse to spend even more time in levels you already like. If anything I might give that to 3D World just based on sheer consistency, since stamps were one of the coolest collectibles I've ever experienced and they were usually hidden.
That being said, Odyssey just by it's nature is usually better at being specifically interesting due to it's exploration. Finding out that jumping off a cliff wasn't an insta-death in Steam Gardens is still one of the coolest moments of this generation for me.
I mean, just last night I was playing Metro Kingdom and found that possessing a parked taxi took me to a hidden zone where you battle and possess tanks, collapsing girders to create bridges, in a storm. Can't think of anything that cool in 3D World.
I mean, that sounds about as inherently interesting as using a motorcycle to outrun a T-Rex. Yet, that moment in Odyssey is one of the biggest disappointments, and that's even on top of the dopamine you get from finding a secret mission like that. It's so bland, so poorly done and just ends up being super pedestrian.