I am actually quoting your previous post, using your own terms. The are relative, but also stand alone... the AR does not have to beat out another platform to have 'simplicity of use'... it is simple. The AR does not have to race against another platform to win either the 'mechanical simplicity' or 'superior reliability' award... either it is, or it is not. You can compare it to another platform, if you wish, but it's not necessary.
Every one of those alternate platforms has a weakness, how you may view that weakness is entirely subjective.
The M1 Garand is not only heavy, but chambered in .30-06. It, too, and along with the M1a, can shed parts (the extractor being one...) and requires a special tool to disassemble and assemble the bolt. The ammunition requires an en bloc clip to load into the rifle... which are not very common... at least, not as common as an AR-15 magazine.
The M1a, like the Garand, is quite heavy, and chambered in .308. There are more parts to maintain on the M1a vs the Garand, but it is not unlike maintenance on the AR-15... the parts are just in a different place. The M1a also requires the bolt assembly/disassembly tool, and a proprietary pair of pliers to loosen/tighten the castle nut on the FSB.
Neither the M1 or M1a have the adaptability the AR does. I don't believe the M1 nor the M1a has the ease of use the AR does. You mention some preppers may not be 'gun people,' yet you turn around and suggest an M1 Garand, or an M1a?
I am not familiar with the M1 Carbine, nor the Mini-14, so I can't speak of them, and I'm only marginally familiar with the SKS. I have had familiarity training with the AK, I was not impressed with it, nor the ergonomics of it (which is certainly a personal preference.)
It's not as mechanically simple as other designs. To pull the bolt reward you use one device, to let the bolt forward under spring tension you use a second device, to push the bolt forward you use a third device. All in different locations, using extra and unnecessary parts that other design use one part for, in one location.
"Simple" and "complex"
are relative terms. The AR is more complicated than other designs both in user operation, and mechanisms. There's no other way to look at it unless you're going to redefine those terms.
How much the increased mechanical and operational complexity matters to you, is up to you. I'm simply stating that it is more complicated than other designs.
And I knew perfectly well a bunch of you were going to jump on the weight of the M1 Garand and M14/M1A, but that's not the point. Both have seen military duty (one still does), and both have been and are owned by civilians. If it's too heavy for you, fair enough. But that does not address the points of mechanical and operational simplicity in those designs compared to the AR. Although the M1 could be argued against based on the internal magazine. Though it is very cleverly designed, it
is more complicated than a box magazine.
The Mini 14 is a scaled down version of the M1A, chambered in 5.56. Rather than an enclosed piston below the gas port, it vents directly into the forestock and functions in much the same way as the Garand, but smaller and lighter. I believe (but do not know) that the M1 Carbine functions in the same way.
The AK is relatively knew to me, but I've field stripped one. It appears to be a very simplistic and rugged design with loose tolerances. All of which we could say about a Glock pistol. It's also an incredibly popular rifle worldwide, fielded by many militaries and militia groups. I'm not sure how many militaries adopted the AR-15/M16/M4 for general issue, but I don't think it's many.
There's a very simple explanation as to why the AR is so common. When the assault weapons ban rolled off in 2004, the easiest way to make receiver was to machine it with a CNC mill out of a block of aluminum. So a bunch of companies sprung up doing just that. And they marketed the heck out of the design. Accessories popped up everywhere, with modular interchangable standardization, and it allowed every owner to customize and tacticool things up all they wanted. Once it became popular, it stayed popular, because a whole bunch of people convinced themselves that it couldn't get any better. And if it did get any better, the better was too expensive.
None of that makes it a good design. It's just a good
enough design, that can be tinkered with and customized, and built at home. That doesn't make it superior to anything else, it just makes it a fun hobby.
If you like it, you like it. If you think it's the best option for you, maybe it is. But that doesn't make it simple either mechanically or operationally, and it doesn't make it the best choice for everyone.
And of course the AR has to beat out other designs! Every time someone choose an AR over everything, it has to do that! And when it does that, it does it by being cheap and popular, and with a normalized reputation as being a good design.