How much DPS does Selene actually add?

[Lyrinn]

this may be off topic, but id like to add that imo a good sch will use Eos and a lazy sch will use Selene.

How about ... no.

Personally, I use Selene in farm content and Eos otherwise, unless it's a AoE intensive fight (e.g. Levi EX) that Eos is specifically better equipped for. Just like how extra VIT is pointless on tanks once they have enough to survive and they're better off stacking STR, Eos is pointless once you have the capability of healing without her.