The use of succor is very debatable. IMO, I believe it acts as a stop gap for the entire raid group from reducing their HP below to a certain level. With that said, I think succor is not meant to be an AoE heal but to make the group stop taking damage while Eos does its job for the next 20ish seconds. (and Medica as well)

I think that while asking on whether succor is suffering any deficiency, you should decide what was succor intended use. Is it to heal the raid or to keep them alive? because there is a difference between the two.