"preparing" a Bole meant a DPS loss. You can call it what you want, FFXIV endgame is just DPS. More DPS is less things to deal with, that's it.
I'm having a hard time believing AST planned Boles for prog (at least, I didn't) when shields (espiecially with a SCH) and mitigation are 1 reliable 2 not a DPS loss 3 arguably more efficient.

As I said, if it popped at the right time, great. On the tank in a dungeon that you outgear, outlevel, so you can perhaps sneak one more DPS spell (if the tanks plays correctly too), fine.
But using all card tools for DPS (be it Balance, Spear or Arrow) was more efficient in the mindset of raiding.
Now if you think healers should heal and buff defense, well you are free to think so. That's not a commonly shared opinion in FFXIV though.