I can see some merit in the concept if it's to allow for more variety in levelling other jobs once you've cleared the content once. It might be a bit jarring to see a level scaled Gladiator or Conjurer in level 30+ content though.

I would appreciate having access to other dungeons when levelling other jobs as it can be very repetitive running the same content multiple times over.

There are also people who don't really care about the story (yes I know, hot take) who just want to run content with their friends and have fun instead of being locked out of it unless they go speed through everything or buy BOTH a level and story skip.

Balance and logistically speaking? I'm not a developer so I have no idea how they'd look at adjusting the lower level jobs for higher end content. I'll hold my peace lest I go into further rabbit holes...