I think the exp% increase that can be rolled on weapons becoming completely useless at max level needs a bit of a rework.
I think this would be a good compromise:
New perk:
While under level 30: grant x% exp bonus
At max level (30+): grants x% bonus crafting materials
This way there is a reason to still want the EXP perk after max level and it is a relatively desirable one you would like to see on a farming set if you are grinding up stuff vs your attempt a level 5 set.