The process of removing padding is called "scrubbing." Tools like Wii Backup Manager or Witguy allow you to do this yourself to your own legally dumped games.
We’ve all been there. You’ve got a 500GB external drive, but after adding Super Smash Bros. Brawl (7.9GB), Mario Galaxy (4.5GB), and Twilight Princess (4.4GB), your space vanishes fast. That’s why the search for "Wii ROM highly compressed" is one of the most common queries in the emulation scene. wii rom highly compressed