I've hit the same issue of slower gameplay when playing the Mario World hacks on PAL hardware. I can see I'm not the first person asking the same question (it was also asked here in 2016: https://www.smwcentral.net/?p=viewthread&t=87343
). It will always be an issue for people in PAL regions wanting to play hacks on real hardware and means a lot of people won't get to enjoy Mario hacks 'properly' this way unless there's some kind of fix.
So, the PAL version of SMW has the game speed cranked up to accommodate for the game slowdown. Audio plays at the same tempo when playing an NTSC version on PAL (I tested) which causes certain audio to be out of sync. The most noticeable gameplay difference is that Mario plays slower, takes longer to get to full speed when running. The sluggishness of everything else (enemies etc.) isn't so noticeable. Hacks are playable and still enjoyable.
As a non-programming layman, my solution for someone that wants to 'fix' the biggest PAL problem would be to make a patch for Mario (the character) to play at his faster PAL speed. Sure, it means that enemies etc. will still move more slowly. I'm guessing fixing all that too would mean patching every other moving item and enemy which may not be possible, except maybe for vanilla hacks that don't change any values of how items and enemies behave.
I'd be interested to see what people's thoughts are of my 'speed up Mario only' suggestion. If Mario's speed values usually appear at the same place in the code in most/all hacks then it creates a better experience, although an otherwise slightly slower and easier game.