"Without specific equipment, the azure/crimson water striders can no longer walk over water. "
This isn’t removing functionality. This is giving you a CHOICE of functionality. If a restaurant changes their menu from offering only steak to steak AND burgers you don’t say they removed options. They added more. If you want waterwalking all you have to do is choose it.
You can’t use a mount below level 20 and 60+ you have flight. So it’s really only 20-60 that are inconvenienced. And I can count on one hand how many bodies of water you need to cross in that level range. That being said, I agree it’d be nice if mount equipment was useable at all levels.
Edit: My ONE concession turns out is already solved by Blizzard: