Stoneskin is not a cooldown rotation. If you did such during the Turn 13 pre-echo days to try to "make up" for a real cooldown during the Flatten cast you would have been crushed to low HP and then die to the following three flare breaths. It required a strict cooldown rotation depending on first phase DPS. Rampart/Foresight, Hallowed Ground, and Sentinel. Stoneskin was the White Mage's job with the 9% buff to land before Flatten hit for extra buffer. If you had done any coil pre-echo, you'd realize how dangerous it is to self-cast a stoneskin over scripted cooldown use. It wasn't just one hit you had to mitigate.

I even get annoyed by the PLDs tanking the knight adds in Thordan EX thinking they are a healer with their two cast skills because that is just more time their knight is still up before the switch, and even not hitting the darn thing while in Sword Oath.

Flash I said for low-level, because you don't have a large MP pool to draw from and if you have to pickup adds because of being careless with stoneskins all over the place in a short period of time, that is totally on the PLD. You don't regenerate MP as fast at low level.

There is even a reason why WAR does cross-class flash in many instances even with Overpower It's because in the chance of having to pick-up adds when pacified there is still a way to run through them and not be helpless for those seconds while they munch on the White Mage.