Games like Super Mario 3d World or 8 player Smash (yes, 4 player Smash is online) could have definitely done better with an online experience considering they are multiplayer games.
Smash, I can agree with, because that's the core of the franchise. However, do tell me how Super Mario 3D World would be better with an online experience?
Instead of having 4 people required to be next to each other, 4 people could play co-op at the comfort of their own homes with strangers or friends. It's not something that would make or break the game, just the fact that a AAA first party top tier game like Super Mario 3d World doesn't offer it is disappointing.