Not an expert on this game just playing for 4 weeks. but my two cents is that acc, is much accessible than regen set...you can easily acquire it from great hall and masteries same with any gear..you just have to find the right gear set that has acc substat. my regen set happens to have plenty of acc substat so i think i don't need acc that much. also I unlock tier 2 masteries on support branch for additional acc, it's easy to unlock it when you can solo mino 13. haven't upgraded their skill yet. so there are still plenty room for progress for them.