I don't play the DMM one so I can only offer what I know from the Nutaku one, so my answer may not be the best as they have more features than ours.
Hercules was probably not a good choice as your first soul, she doesn't provide you with any utilities needed. If anything, she's just an extra you level for the mastery bonus. As far as I know, dark and thunder lack b-frame debuffs. While dark does have Dark Amaterasu, she is time limited plus SSR making her difficult to get in the first place, and one from the Koihime event is only obtainable from the event itself, unless DMM recently had a rerun of it and you do have her, then you can start your dark team. Thunder has absolutely none. This means your soul needs to fill the spot for this, meaning grabbing D'art would have probably been a better choice for Sniper Shot or Mordred for at least Outrage for a weak b-frame and for Black Propaganda then back to D'art.
For your team itself, the general goal is to eventually separate out your elements into single element teams, proper weapon grids for each, aim for -40% or more atk/def down debuffs, some heals, overdrive extenders and whatever other skills needed for the current content like debuff recovery or dispelling enemy buffs.
As it stands, you're heavily lacking debuffs, even with the mixed party, all you have is 2 def downs. I don't know what other himes and souls you have so I can't really say anything more.