Damage output too low? What? SSR Artemis purpose is to increase your overall party output and to replace the weaker units like Diana or free your soul from using Ambush. Not sure where you're getting this low damage output from. Heck, she could even replace Tsukuyomi.
Yes it would be an increase as Micheal is there as offensive support while Raphael is there to help control overdrive/rage.
While Eros is good at mitigating some damage, the problem with her is you rarely see any major bosses that hit weak enough that her barrier shows its worth. Bosses either hit so weak it wouldn't matter if you had used it or they hit so hard it won't save you. I find her to essentially be a poor mans awakened Gaia. The -20% atk debuff is always good to have but for a light team, it's very easy to hit cap as they have multiple sources of atk downs.