GNB has been overpowered for a while now. I think it's held back in CC by limited swapping opportunities, but that isn't really an issue in FL and RW and unsurprisingly it's straight S tier in those environments. GNB is tied with PLD for tankiest tank in tank stance and is basically a slightly less one-trick MNK in DPS stance, and healer stance is fantastic for games where attrition is the name of the game. Being able to swap between all three depending on what's needed is extremely strong and is the largest part of why GNB is overpowered. If they ever changed D&J to allow on-demand stance swapping, GNB would become the new BLM overnight.

It's just Square proving they're not equipped to run an actually competitive circuit. Their method of balancing/tweaking things has largely been based off of popularity or perceived strength, not actual math. DotA had a problem with this for a while, too.