I like the idea of overlapping leves! That sounds epic and like great gameplay!

"Start X combat leve, get 1. Start Y gathering leve, get 2. Start Z crafting leve and use 1+2 to get EXP/item" and that could be done without having to bottleneck it behind leves.

One of the things I've learned is, while I wanted to level everything together, I didn't have the levels for that. So I started working on one specific job at a time and it seems to be more the way it was intended to be done.