[Broco]

When I think about SMW versus SMB3 I mostly think about the overworld innovations you mention in your last paragraph. While the individual stage design is lackluster compared to SMB3, the new overworld structure does so much to contextualize and pace the stages. No other Mario game has done that better, and to me those meta elements manage to have a larger impact on overall fun than the difference in stage design quality.

SMB3 is a marathon. Your reward for completing a stage is the next stage. The stages themselves are varied but they monotonously come one after the other. The only way to change the order is brief alternate paths or using the flute, which feels like I'm cheating myself of content. If you run out of lives it punishingly resets the completion state of stages in the current zone, which discourages using the flute anyway as you might end up stuck. You can't save and have to start from zone 1 every time, so I've played that about 20x more often than the later levels (as a result of visiting friends as a kid and briefly playing SMB3 -- I didn't have my own NES). SMB3 is twice as long as SMB1 and it stretches that mostly linear, no-save, limited-lives superstructure further than fully makes sense -- its own overworld innovations don't go far enough. It's always felt like a bit of an exhausting slog for me.

In SMW you can vary up the pacing as you like by popping into star world, going back to a red dot to find the secret, trying the alternate route through world 3, and so on. SMW's foundational principles are alternate paths, secrets and more generally the joys of curiosity and discovery. The best moments are things like completing a ! block palace and then running back excitedly to where you remember an outline of that color to find the secret behind it, getting trolled by the game in world 5 as it keeps looping you back to the previous stage, or finding that the world 6 secret pipe sends you over the cliff in the top left corner of world 8. It delights with an "even more secret world" hidden behind the hardest secret of the secret world.