I would worry about that if Holy wasn't nerfed to poop.
Hate to break it to you, but holy spam is no longer a very potent combo and WHM (and BLM) will always be behind SMN now.
Non-PLD tanks can pull REALLY close to the DPS (and lol ahead of NIN) in AoE if they know how to maximize their AoE. I used to switch between VIT for big trash pulls and STR for bosses. But I realized the difference is minor and all that I need to do as a tank is utilize CDs.
Also you spamming holy will stun the adds anyways so it doesn't matter if I wore VIT, STR or my swimsuit bikini for the whole 6s that the mobs are stunned.
Oh, the thing about Holy though is: Spamming it will drastically reduce the duration of the "stun-lock" since it'll clip after the half duration thing. And spacing out Holy to max out stun duration is a DPS loss. Make your choice.