Zardnaar
Legend
I suspect fixing 3.0 would take less work than updating AD&D. I'm doing a little work on that now, but I'm only at the start and I haven't playtested anything. Right now it's comparing how 3e does things compared to earlier editions and trying to find a match in the 3e rules for stuff that was dropped (and often it was 2e that dropped things rather than 3e I'm finding.)
I've tried doing both fixing AD&D is easier.
Hell ascending ACs and B/X ability modifiers go a long way right there. Plug in 5E or tweak 4E skill system you're mist of the way there.
Fixing 3E basically requires a rewrite. Depending on what your goal is replacing the skill system and a unified numbers progression woukd be a good place to start.