Even if Selene is only a 2-3% raid DPS increase (which I disagree with, the number is probably a larger variable depending on your composition), that's 2-3% more DPS. That's worth a lot more than Eos's AOE healing in certain situations.

Honestly, just use your head and learn to use both, even in the same encounter. I no longer use Eos outside of certain phases in T9 and T8, because the AOE healing brought by her is not at all necessary and the slight DPS increase brings more to the table than unnecessary overhealing.