I only used the 7 deadly sins for xp ascending. Farming xp on floor 100 with 6 deadly sins equipped was easy and gave me the full 200% xp bonus. I just put a quest stone on each piece. Just hit level 98 on my last ascension and dumped it all, and I'm going back to floor climbing and I'll get my last level somewhere in the 800s. I wanna climb to 1k, finish my hero levels (I'm at 95 right now) and then farm up some crystals to make a PvP set since my PvE set is complete.
That said, I'm sure there are other uses for the 7 deadly sins set, but I don't think it does anything better than a crafted set. I think its just a nicely balanced build for PvE.