So the solution is to replace it with a bland, painfully generic NSMB hub (outside of the carnival level)?
Instead of giving that hub purpose and have quests intrinsic to it, like Super Mario Sunshine?
Why even bother at that point? Just make it level to level next time.
It's not really a hub. It's a SMB3 style map with a bit of spice. They needed something to stand as user interface that allowed players to choose from multiple routes and find non-level stuff. A straight menu would be too minimal. SMG2 already did the same thing, but more restricted and less visually exciting.
But the point I was making is that 3D World has more content than other 3D Mario games, so how is it lazy of them to not make a hub? They just spent their time and energy elsewhere, like making levels instead.