The thing is, you cannot just look at PLD's burst phase and go based on that, that was the original misconception which lead to the 2 Divine Holy Spirits per FoF window, as that was the highest damage. You also have to look at the rest of the rotation as dropping Atonements is wasting potential damage and if you delay your combo with Holy Spirits, you delay atonements, which could mean lower damage potential compared to just following the priority system.

This does, of course, assume 100% uptime on a boss and if you do disconnect for any length of time, either Divine Holy Spirit or a hardcast Holy Spirit is going to be optimal, just because you are keeping damage up where you otherwise wouldn't.