One thing that I do find a little odd with Holos is that it's an AoE flat heal + damage reduction on a long cooldown. You kind of need to use it at very specific moments to get the most out of it. I can't use it before an attack like Kerachole because then I lose all of the healing rather than get that healing from a regen that ticks after the hit goes off, but the damage reduction won't reduce the damage you're immediately trying to address. More optimal use of it will come down to fight knowledge and using it right after the first hit of a high damage phase.