He's talking about weapon skill level, not hime level, though you need to work on that too because Lv25 isn't gonna get you anywhere, you're not even half way to their max level.

People don't use D'art's tree for her for the drop rate increase skill, which has barely has any value worth using, people use her for the -atk/-def debuff.

I've said this in many topics but just because you have several SSR himes, it doesn't mean you should just throw all of them together in the same party. You're extremely gimping your damage by having that many different element himes.