All the heroes you mention struggle with being balanced while remaining useful and being able to be used as intended. That’s the point.
As for Vox, I’d give him minimal AA energy cost and low to moderate ability cost, with a moderate energy pool and somewhat low energy regen. That way, the items he buys can improve his energy regen and energy pool to moderate and high respectively, and by endgame he can still spam his abilities as he can now, but EVENTUALLY he’d have to back out. (AND If I could REALLY change him what I’d do is I’d buff his defense a little, change his resonance to be an ability that weakened with your distance from Vox, changed each bolt to set a minor slow on hit, and his B to be a slightly better slow, ult to be an ability where he channels and sends out a pulse that snaps all enemies out of resonance, but all enemies still in range take damage scaling off at the furthest ranges and take status effects of increasing intensity nearest to Vox. The closest enemies take the most damage, are stunned momentarily, silenced, and slowed, the enemies further out are only silenced and slowed snd weaker, but to compensate, these effects would decay more rapidly BUT that’s off topic.)
I’m not saying Baron is not fun to play. I’m saying when you’re having fun playing him, everyone else usually isn’t having fun playing you. And when you’re not effective with him, everyone else usually already is to some degree. Celeste and Varya also struggle to be balanced as they are both also massively difficult to play against late game for everyone, whereas hypercarries without aoe don’t get that designation: ranged hypercarries with aoe can still beat them, and the guy next to them. Late game scaling mages that don’t have aoe? Not a lot. That’s why they’re not fun to play against when their aoe is powerful. Big difference between a Baptiste Ult and a Celeste Ult. For that matter, big difference between a Celeste A and a Kestrel A when it comes to teamfights.
If you’re not an assassin, you shouldn’t be a hypercarry. That’s the point. Hypercarry means you multikill quickly but you don’t have to do it all in one shot. That means you should be dying quickly as well or nerfed in some other way for balance purposes. AOE ranged hypercarries defeat this because if you’re aoe and ranged you should be nerfed to only have the ability to do it every once in a while or you should have some other weakness limiting you from multikilling any time you want, otherwise you alone are decimating the enemy team. A carry should be weak. That’s the point. Having range inherently makes you stronger. Having aoe inherently makes you stronger. Having power on top of that just makes it cheese unless that power is contained in some way, like Baron’s channel time for his ult and mortar air time. And he can still decimate scores of people by himself if he’s good late game, while having inherent advantages, making him inherently toxic if he’s built in a fun way for the actual player playing him, unless that player has to use skill, balancing the playinf field, which timing his mortars and his slow rocket speed is likely intended for, but the skill ceiling for them is disproportionate to the damage they do, which is why Baron is built so difficult to capitalize on until so late in the game and heroes like saw struggle to be balanced. And no, hypercarries that are simplistic to use should be simplistic to kill (like saw). Hypercarries that require skill should be given better means to defend themselves and great means of attacking but still be inherently nerfed in some way like defense or energy availability, since they usually need cooldown (like reza and anka should be). And they should still be easy to kill healthwise even if you need skill to get at their health (like taka and Baron with Jumpjets).
If you are none of those things you probably shouldn’t be a hypercarry or you’re probably not making the game fun for othe players in an inherently overpowered way.