To me, the cape highlights everything that was wrong with SMW compared to SMB3. The thing that I love about SMB1 and SMB3 is that the controls are extremely simple -- you almost never have an issue with a learning curve, no matter what is going on. And, as the levels get more difficult, you can rely on how they always act. It makes experimenting with what is really a limited set of tools to find the secrets that much more rewarding.
With SMW, between the cape and Yoshi just for instance, you have SO much needless complexity. You're right -- if you're good at the cape you can practically fly from one end of the level to the other. But that is what bugged me and still bugs me about the game -- you had to overcome a serious learning curve for the special things to be able to use them to the full ability. Instead of walking up and knowing exactly what that particular item does, you have to remember what color Yoshi does what and so on.
From the first moment I played SMW, it bothered me that they took the series in that direction. I still find it a decent game, although no where near as good as SMB1 or SMB3.
Back in the day, I also thought that Sonic had a ton of flaws. It was fun to watch, but felt like total luck when playing it. I never liked that the speed impacted your ability to react to things, and it became all about memorization.
It wasn't until Donkey Kong Country that I really felt like this was addressed well by a platformer on either console. So, to me -- the answer for this question is neither.