What I usually see is 2-6 on expert and 4-8 on ragnarok. At least the ones that I join. It should be very unusual to have raid fail if you request help from all, since people are farming it like crazy and joining whatever they can.
As for me... I can auto skill solo both experts with water team, but in order to be on safe side I need to take Jorm as supporting eidolon since my healer is Nike and Jean is my soul, so that extra hp really helps when she is going nuts with AoE spam.