I am going to get into the weeds a bit in this post, as you seem confused on some specifics of what the others were talking about. As such, I don't know what knowledge you have or concepts you are familiar with... So I am breaking it down to basics here.
An AK... They can be reasonably accurate, or horrible depending on the quality of the individual rifle.
From what I have seen... A lower end AK may be capable of groups of 4-6in at 100yds. If you get a more mid-range rifle at around the $1000 price point, I see people's reporting between 2-4in at 100yds as an average. The really nice AKs that run $1500 and up, they can get 1-2in on average. This is all just a rough average, and some rifles may do better or worse. This is also basically pure mechanical accuracy. The skill of the shooter and their chosen aiming device will come into play. (AK iron sights are not as precise or easy to use as other options)
In contrast, the average accuracy for an AR in the $600-800 price range is 1.5-2in at 100yds. I have seen worse though, and some low end ones may be 2-4in... Spending $1000- 1500 on an AR is no guarantee it will shoot significantly better than 1.5-2in, but the higher end ones usually do 1in at 100yds on average from my experience and repots online.
Ammo quality plays a part here... Cheap ammo results in lower performance, which is why AKs can get a bad wrap on accuracy, and the fact that a lot of guys just get lower end rifles too. So between a mediocre rifle and crap ammo, good results are not to be expected.
That being said, a decent AK will be able to hit a man size target at 300yds, using milspec ammo, without much difficulty if you have the skill to use it.
Bullet energy and capabilities are very important for a SHTF situation... If you are truly in a direction situation, you want your chosen weapon to be effective. Any weapon can be better than no weapon, but if you have the choice, you want to make a good one.
A 9mm even from a PCC is a poor performer at stopping threats. (Basically all pistol calibers are poor performers) Pistol calibers are easier to suppress, which is why they were popular in small sub guns for so long. And the only reason sub guns where created in the first place is to make a small and easy to control full auto weapon for relatively close range work, to supplement the rifle teams using full sized rifles... Being full auto helped make up for the lower effectiveness of the pistol calibers, due to being able to put several rounds into the target very quickly.
Back in the early 1900s the concept of an intermediate caliber wasn't a thing. So they had full power rifle rounds like 30-06 and pistol rounds like 45acp. 30-06 did not make for an easy to control short range full auto weapon. So the subgun was born. The sub gun concept remained popular for decades after, but have relatively recently gone out of favor for small and light SBRs for the units that used to use sub guns. Modern advances have pushed the subgun into a smaller niche.
Rifle bullets have more velocity and energy. And yes energy is important, as the energies and velocities of rifle rounds are high enough that you see secondary wounding capabilities that pistols do not have. So a rifle round can be effective even if shot placement isn't perfect.
They also have higher sectional density and more aerodynamic shapes, which means they lose less velocity and energy as they travel, which gives them even more advantage over pistol bullets at longer ranges.
And a PCC isn't a subgun... It can not make up for it's lack of power with volume of fire.
This is a very important consideration if SHTF, or simple home defense, is a role your weapon is to fill.
Here are the basics on accuracy, aiming, and distance...
There is bullet drop... This is how much the bullet falls (drops) from the line of sight, due to gravity, as it flies though the air.
Everything falls at the same rate in relation to the time in the air, so going faster means you can go a longer distance for the same amount of drop. A rough way to look at it, though not perfectly accurate due to the nature of how gravity works... Is that something going twice as fast, will go twice as far for the same amount of drop.
A 9mm from a PCC is much slower than a 7.62x39, so the amount of bullet drop at a given distance is greater.
This matters because it affects the ballistics of aiming. With something like a red dot sight, or a scope that does not have a bullet drop calculated reticle, you would be forced to "hold over"... Basically you would have to adjust your point of aim on the target, to get the bullet to strike where you want it to.
For the 9mm zeroed at 25yds, you may have to aim a foot high to get it to hit the bullseye, and maybe 2ft high to hit at say 150yds.
Rifle rounds are faster, and "shoot flatter", meaning you need less hold over at a given distance. The ability to zero at a longer range helps too.
Something like the 55gr 5.56 zeroed at 50yds has a ballisic profile that allows you to aim at a given point, and only deviate between 2in high and low, from 0-250yds, and only needing something like 4in of hold at 300yds. Basically, aim center of mass all the way to 300yds, and you will make an effective hit. 7.62x39 isn't as flat shooting though. The ballistics of 7.62x39 have much greater drop, so the round is most effective at 300yds or less,as the rate of drop gets very high past that. And the energies drop of quickly as well. 5.45 and 5.56 are better for 300-500yds. In general they are good performers on the whole, but the 7.62x39 does hit pretty hard inside 150yds compared to the other two.
Accuracy... Many times we will say something like, "this rifle can shoot 2in groups at 100yds" and that is all well and good... But firearm accuracy at least for rifles, when we are talking 100yds and more... Is really measured properly in Minutes of Angle or "MOA"
MOA is an angular measurement. The point/source of the angle is the barrel of the rifle.
1moa is basically 1in at 100yds. It's mostly just a coincidence that 1moa is roughly 1in at 100yds. The real measurement of 1moa isn't exactly 1in at 100yds, it's actually slightly more. (Most shooters can ignore the small difference. It does matter more to precision shooters of high skill though, as the difference adds up as the distance to the target increases)
The nature of an angular measurement is that the distance to the target matters as to what size the physical group on the target is. This is because as two lines, separated by an angle get farther from the source of the angle, they get farther apart.
Meaning a rifle capable of 1moa accuracy will shoot a group of 1in at 100yds, and it will shoot 2in at 200yds, and 3in at 300yds and so on. The same rifle will shoot a half inch group at fifty yards, and a quarter inch at 25 yards. 1moa increases in size by a quarter inch for every 25yds.
Another example is a 3moa rifle will shoot a 3in group at 100yds, and a 6in group at 200yds, so on and so on.
This linear increase in group size relative to distance Is strictly on paper though. Based on perfect conditions and no variables. Shooter skill comes into play as well as the ammo quality. Most shooters will not be able to hold to the same level of accuracy as distance increases, due to the increased difficulty in consistent aiming. Ammo quality palys a role, as small variations between individual bullets themselves and the loaded cartridges they are part of, will amplify as distance increases. As the distance gets even farther, and the bullet slows down, the change from a supersonic speed to a subsonic speed can cause instabilities as well.
Rifle rounds with their higher aerodynamics, and increased sectional density, are inherently more accurate than pistol rounds. The difference is just more apparent at longer ranges.
Many PCC are only capable of several MOA at 100yds, and their lower aerodynamic efficiency means they tend to get worse at longer ranges. So say... 3moa at 100yds may turn into 8moa at 200yds.
Also... You want a rifle capable of handling rough conditions... But you are dismissive of the AR...
They are no where near as delicate or as finicky as many think. They can handle a lot of abuse and tolerate getting pretty dirty too. Just Google "filthy 14" for an account of an AR going many many thousands of rounds with no cleaning, and working just fine.
Sure, an AK may handle a little neglect and lack of regular cleaning and lubrication better than an AR... But if you can manage to wipe off the BCG with a rag and apply a little oil (old motor oil would work fine) every now and then... The AR will work just fine.
