When it comes to dark side TB I know that raw GP matters more than combat missions. I don't need to complete all 4 waves for my guild to do well however having that said I do think that wave 4 past phase 3 is too strong.
Gear 11 characters go in the fight, apply their damage and debuffs due to pre built turn meter and barely make a dent. The battle is full of healers/cleansers and defense up buffs. All of your work to apply a ton of debuffs cleansed within a turn! Then they start their attacks and basically 2 shot gear 11 characters, even gear 12 characters. They gain turn meter also so they can whipe out an entire team with 1 rotation, literally! It's actually happened twice to me today.
I think it's kind of unreasonable that you spend a full rotation with a zeta lead Palpatine, dropping debuffs all over the place, watching g12 Vader hit an enemy with his culling blade and with about 6 debuffs on them and not even going past half their protection. Then they take their turns and then run is over!
You need characters like Thrawn and Nihilus to stand a chance and there isn't enough of those to go around.