Yoshi-P doesn't really like the weapon gating and classes from what he's said, think those systems just stayed in for the sake of saving development time. Keep in mind if you remove cross class skills at this point in the game you have to either rebalance numbers around the lack of said skills or make entirely new "similar" ones for every job that could use that. You can argue that "well they can just use the current ones" but in that case would cost em alot less time to just leave it as is.