Don't get me wrong, Devotion is one of the weaker synergy buffs of the ones available, however, it's only that weak in a party that poorly uses it. Devotion's higher in a reasonable synergy comp with solid play.
The heal's definitely not laughable and is something healers can account for when optimising. But it's not something we will play around healers for. FBT happens when it needs to happen, not when healers want EF.