Well, the charge isn't going to disappear as soon the moment that Kars Sops breathing. So since that Cell destroying poison is made of Muzan's blood, it get destroyed basically instantly thanks to the Hamon that's still present in Kars Flesh. Considering that Kars Hamon is so strong that it flat out melts normal human flesh, it's highly likely that it would severely **** up Muzan beyond just destroying his tentacles. It's also entirely reasonable to say that Muzan's tendrils would disentegrate before they have time to physically damage Kars.
Even assuming that Kars will get ripped to shredds, each of those body parts will be fully capable of growing a set of Lungs and charging themselves with Hamon.
As far as projectiles are concerned, Hamon Man technically includes Straizo, who could fire off laser beams with his eyes
Okay, your contention is that with whatever small amount of breath that Kars gets in the instant before Muzan's tendrils rip him to pieces is going to be sufficient to suffuse his entire body with Hamon of such intensity that it will not only completely destroy Muzan's cell destruction and his physical flesh and apparently prevent him from being harmed?
Also, Muzan could just use his invisible spiral projectile to blast Kars to pieces so it's not like he even technically has to touch him. He can also shoot lightning that inflicts a demon blood art that attacks the nervous system if he's getting fancy. He has a lot of options here.
Like, bell rings, Muzan blasts Kars with lightning or with his spiral projectiles. Kars is now in pieces on the floor and has to try and regenerate. Muzan just keeps blasting him for a ten count.
And like, the speed is a massive issue here. Kars' best speed feat is parrying Stroheim's bullets which makes him, at best, as fast as one of the Hashira prior to them discovering their mark or entering the see-through world. Muzan is capable of fighting four people /above/ Kars' level at the same time, backed up by three invisible additional opponents who clock in at around or just under Kars' level simultaneously while rapidly aging such that he is physically experiencing a year of aging every second.
As he will not be poisoned in this match, he won't have issues of stamina and his speed will remain at the absolute peak of his powers.
I really don't see how Kars is going to overcome the sheer stat disparity here.
Okay, so Muzan might be much too powerful.
How far along does Hamon Man go up the 12 Kizuki, Nik?
Erm... better.
Speed is broadly much more equal with the exception of Upper Moon 1 who was fighting multiple Hashira, including Himejima when he was going into the see-through world, so he'd have an edge.
The other Kizuki don't have Muzan's freakish resistances. Beheading still kind of works, Akaza and Upper Moon 1 notwithstanding. They are also going to have a harder time keeping him down because they have way fewer attack options.
Doma might actually do well here, his freezing abilities should be a neat counter to regeneration.
I mean, would they really need to counter the kizukis' regeneration when none of them had any real resistance to sunlight? I guess maybe it would make glancing wounds less likely to maim. Was Kars able to mimic his subordinate's abilities, like going invisible or having super hot blood?
Ina scenario fight, compare Hamon users might be able to arrange an airstrike on Muzan's location is Kars just hijacking a fighter jet and using Hermit Purple to find Muzan's location.