ok so there are actually a lot of differences and this is exactly why you cannot submit a run on switch on the SMG leaderboard (about ILs we already asked to add them on the 3das category but it might be really messy this is why we don't have them, honestly not a huge loss imo)

First the load times, as you previously said they are way faster than the wii (~3 minutes just for any% and over a minute compared the best way to run the game currently, which is the JPVC version on the Wii U)

Second is that you can run the game on korean and this is where the biggest difference is. We banned Korean a few years ago because it was the only version that didn't get one as a Virtual Console after, so it was unfair (and also impossible to submit theoratically). Now in 3das the Korean has been readded and you can run it, it saves time over the Japanese language and with the switch loads it becomes just completely broken comparing someone who runs on an English Wii and a Korean Switch (~4 minutes)

I hope I could've help you if you have more questions you can dm me :)

Yes, the WiiUVC is the title of the e shop. If you use the Wii menu with the disc this is like the Wii version because you use the same menu and that is like a Wii.

But I don't really know if the loading times are faster on Wii U...