Got my MNK to 80 and here are my thoughts.

People have oversold GL4. The speed increase is in hundredths of a second which is marginal. With AF4 gear, the Skill Speed is so low you need to get up to GL4 to have a GCD as fast as the end-game BiS gear for Stormblood, meaning you're not actually going faster, and you need to do an extra step to get to the same speed, meaning it takes longer to wind up. Combine this with the removal of damage-dealing oGCDs and that means you have less to do while going just as fast, making it feel slower to play. Potencies may have been changed to adjust for this damage-wise, but the result is that it's far more boring to play. It's still a problem if you have more than 2k SkS on your gear. The lack of oGCDs just makes it still feel like there's nothing to do in specific windows with forced slowdowns. This makes MNK boring to play and is not what players had in mind when GL4 was revealed. Their desire was to go FASTER, not to take longer to get to the same speed with less to do.

It feels like the job was largely tuned for dungeon encounters with a better AoE rotation, but single-target gameplay suffers. Anatman is a worthless skill. It only maxes your GL duration if you go up a stack of GL, which can only happen while you're already in combat, meaning you'd either have to lose DPS up-time to use it or save it for a phase change. There is not a single phase change in the game outside of o10s that is so long that Six-Sided Star and/or Riddle of Earth couldn't just be used instead for these purposes. O10s having an obnoxiously long phase change which doesn't deal damage quickly enough for you to use RoE is an encounter design issue and a rare one at that, not something MNK needs a tool to deal with. It doesn't generate GL stacks or maxes your duration when you're not in combat, and requires at least one GL stack to do anything, so it can't be used for pre-pulling. If you're already at GL4 it won't max your duration, so if you use it for a phase change and you have only a few seconds left on your GL timer, it just freezes the timer.

I'd much rather have abilities which allow me to regain a GL stack while maintaining DPS uptime than being forced to use this. It feels only useful for pausing at a dummy, but otherwise impractical and there are other, better skills which do the same things for GL stacks and don't take you out of the fight, which makes it redundant and not as helpful/useful.

I'll post my proposed solutions right after this because of the character limitations per pose :P