Tank damage depends on how many stacks the tank has. Tank swap at 3 stacks and there should be no issues with healing tanks.

Final phase can be hectic, it becomes a DPS check rather than a healing check. Its quite similar to Demon wall in terms of - dps must kill the lazers fast or it can wipe the party. The faster lazers are killed, the easier it is to heal and the less likely you'll have deaths. Switcast medica 2 is a really big deal on this fight.