Having to keep your attention on the party list and the fight mechanics at the same is in essence what makes any end game fight difficult for healers. I can't recommend you just "ignore the health bars". There are a few tips that can make being aware of indicators much easier, others have mentioned these already.
Turn down your bgm in settings. While leaving sound effects up.
Turn off party member's battle effects, when everyone is stacked it can distract from the divebomb indicator.
Focus target the boss, and adjust your hud so the ft bar is next to the party list.