I've been thinking about the "Young" tag lately, as art that I've been favoriting has consistently been filtered by my blacklist due to art being tagged as "young", even when the characters depicted are clearly adults. Grey areas, such as Pokemon, also muddy the waters on the issue, which makes this situation all the more frustrating.

There is also the risk that this tag could result in unfounded controversies with artists that (hopefully) don't create cub art. For instance, I've noticed that uploads for Zackary911's art have caused some unfounded backlash for the artist based on the comments for the uploads themselves (https://e621.net/posts/5256475?q=zackary911+young).

As there are a few uploads currently with an "adult_(lore)" tag enabled. I think it should be more sensible to use an "Underage_(Lore)" tag for cub art, so blacklists can be more refined and images that involve adult characters aren't blacklisted due to broad-reaching tags.

Anyone else have any thoughts like this?

young_(lore) exists for when characters are canonically young but do not look like it

What you're suggesting is not how lore tags work, many exist to correct issues caused by TWYS, hence adult_(lore)

This is literally the exact opposite of the way lore tags are meant to be used. What you are describing is best handled as young adult_(lore), which we already do.
Anything that doesn't involve keeping young tagged also creates an incentive for artists to draw young characters and then claim they're some arbitrary age like 60, 1000, etc. in order to get increased exposure.