I really like the new Reprisal. It rewards good timing, and it feels like you're actively mitigating the attack. If you want to add some potency to it, just give it a Radiant Shield type effect that punishes the mob for doing damage while it's active. Make that Ravensbeak-style explosion count for something.

Unlike with damage buffs (i.e. Slashing, Piercing, etc.), total uptime isn't all that important for raid mitigation. Your effective uptime matters (i.e. do you have it up for every big hit?) Even having 100% uptime on Reprisal doesn't really add anything extra if you can simply rotate between DV/SiO/PoA on each big hit.

What makes the new raid mitigation moves scary is that they have the potential to approach Tank LB1 territory, if not surpassing it. I think as a rule of thumb, raid DR should not exceed 10%.