I do get the point of having at least one way to hit single target. Not everything is standardized dungeons and 8 man boss fights. Deep Dungeon particularly is an environment where tools like Tomahawk, your Glare/Broil/etc, Heavy Shot, and so on would make things more challenging if everything was an AOE. But all you really need in those scenarios is a way to pull an enemy into the hallway. Excluding examples like Standard/Technical Step or Earthly Star which are really large AOEs, your normal AOE attacks aren't going to clip dangerous enemies in a deep dungeon because if you're that close to an enemy you don't want to be fighting, your choice of battlefield is the real thing we need to question.
But beyond that fringe example, AOE just isn't really an interesting factor in this game 99% of the time. Having the choice between single target or AOE is only meaningful and interesting when the game regularly presents you with opportunities for single target and AOE to both hold value at the same time. So rarely do we even have interesting fights with more than one enemy to target. Hansel and Gretel come to mind, a pair of bosses with mostly fixed movement that will sometimes come together, but even then, a lot of AOEs are barely any gain on 2 or more (and some are even still a loss on two). Oh, I gain an extra 10 potency for using Dyskrasia over Dosis? Woohoo... Lucky me.
Thats why outside of a select few actions, I don't see why we shouldn't just merge every AOE with the single target version of the same thing. Make the potency on the first target the same as it currently is, and pair that with damage falloff on subsequent enemies. Would Monk not be exactly the same if Bootshine, Twin Snakes, and Snap Punch naturally upgraded into Shadow of the Destroyer, Four-Point Fury, and Rockbreaker, respectively? You still have Dragon Kick, True Strike, and Demolish as single targets. It's just instead of your AOE combo taking up three more hotbar actions, its just one of your two combos instead. You could also make Enlightenment an upgrade of Forbidden Chakra and save another spot on the hotbar. And those 4 extra spots can potentially be used for something new. We don't have to just purge things and leave it at that.
Or instead of merging two actions, give a purpose to the AOE action that functions in single target. An example i've gone to before was have Dyskrasia's potency be the same as Dosis on the first target with reduced damage on other enemies, make the MP cost 800, and make it a ranged instant cast attack. Now Dyskrasia is still the attack you spam for AOE, but it doubles as Sage's mobility tool. If you don't need to move or weave, Dosis is half the MP cost. You get more agency in how you want to utilize mobility.