You are totally missing the point. This is so beyond relevant to the core of this discussion. It doesn't become over-powered it becomes more powerful.
1 - X class should have this because Y class has this makes no sense. Because BLM get Flare should MNK get an AE move just as powerful? This holds absolutely no water as an argument.
2 - SA is the only skill in the game that gets a frontal bonus, because it is part of the ROG class about sneaking. Can a MNK sneak? No, so they can't do a sneaky attack that does extra potency from the from.
3 - You DO have a frontal option, you can do ALL MNK attacks from the front. ALL OF THEM. THEY ALL WORK.
No. You don't get to tank in special circumstances. You don't get slightly reduced damage from the front in special circumstances, you get severely penalized. MNK is completely fine as it is with potency in the front. The only time they are in the front is if someone screwed up or you are soloing. If someone screwed up you pay the penalty for that. If you are solo you certainly don't need increased potency because all of the open world content is easy. SA is a ROG skill for the ROG playstyle, the fact that it exists has nothing to do with MNK skills.
You're suggestions will not "over power" the MNK but its completely unnecessary. IT IS ALREADY MADE WEAKER FROM THE FRONT. THIS EXISTS.
You're assuming accuracy in this game works the exact same as accuracy in other games. In other games, 100% accuracy is impossible, so making you miss more is equivalent to decreasing your potency.
You're points of "just make it weaker from the front," are ALREADY IN THE GAME:
Bootshine - Front: 150 | Rear: Auto-Crit
Twin Snakes - Front: 100 | Flank: 140
Snap Punch - Front: 140 | Flank: 180
Dragon Kick - Front: 100 | Flank: 150
True Stike - Front: 150 | Rear: 190
Demolish - Front: 30 | Rear: 70
/head explode