Stoneskin 2 was a patchwork fix to the fact that every time you wiped you couldn’t pull till the WHM stood there and cast Stoneskin on every party member individually

There was also Stoneskin 2 in legacy that got removed in 1.2 after they just bestowed Stoneskin 2’s effect to Stoneskin 1

So essentially Stoneskin 1 in legacy was a 6% damage reduction to everyone and Stoneskin 2 was 12%, then they made Stoneskin 1 12% in 1.2 and deleted Stoneskin 2, then in 2.0 Stoneskin 1 was changed to only affect a single party member for 12% and because that got backlash due to prepull they re-added Stoneskin 2 which was AOE Stoneskin 1 (or the original version of Stoneskin 1 from post 1.2 or original Stoneskin 2 from pre 1.2)