Youre correct on grit. dropping grit didnt consume a GCD. The same is true for Shield oath, too. The only difference is that when DRK dropped grit, they already had darkside up. PLD still had to use Sword Oath regardless. I remember a big thing for PLD was to either eat the GCD to swap directly into sword oath, or to simply drop shield oath and try to weave in sword oath when you were forced to lose uptime anyway, like a ranged phase or when a boss went invuln.

stormblood kind of made that a little.... bad to do though, because dropping shield oath killed your gauge in it's entirety
Hadn't actually thought about the whole "drop ShO and swap SwO during downtime" thing, haha. Probably because my mind simply never thought about dps optimization to that severe of a degree.

But yeah, I'm guessing there were some people that did that. Because PLD's gauge wasn't/isn't actually used for anything except defensive maneuvers that don't actually contribute to your damage dealt... I'm sure that to some people it was deemed acceptable loss -_-