I think a good solution would be to simply buff the Heavy Carronade back to it's original form, with or without the old Heavy Clip is up to debate. It used to be that Heavy Carro was amazing at balloon popping and DPS, whilst hwacha had okay DPS and disables, and it's effect became more useful the closer you got, which is why muse buffed the Hwacha's jitter in the first place after nerfing heavy clip, and while that was pointless, my point here is that now, the situation has turned upside down and Hwacha is the more powerful close range heavy weapon in comparison to H.Carro. Now if you nerf Hwacha's effectiveness in any way, what you have then is 2 weaker heavy weapons and you've officially ruined close range heavy gun meta in a sense by making it unable to deal dps on it's own and unable to provide the desired effect with ease. So before you give any nerfs to the Hwacha you'll have to buff H.Carro.
What I'd propose then, is a collection of opinions that I've gathered from conversations with different vets. Revert every single nerf Heavy Carronade has recieved except the Heavy Clip nerf, return Hwacha it's old jitter, and remove the -25% clip size penalty from the Heavy Clip. I think the difference between old and current heavy clip here is that it takes a few more shots to do the same effect - but those few more shots just aren't there. You dont want to penalize players' ammo capacity just to tune their accuracy up a bit rather than making them shoot straight. And this way, Hwacha would still have a way to coexist with other guns midrange too - but without the annoyingly wide Burst rounds range, whilst Heavy Carronade could exist as a DPS and balloon popper aswell, but without the old 400m balloon pops unless you're using Loch, which is always a fair tradeoff.