I'm all ears, though, would love to hear someone articulately explain (without any myths or hyperbole) what the "trade-offs" are, how the design could be improved beyond what multiple mechanical engineers have done without actually making it needlessly complex.
If we accept the basic gas tube/key/carrier as a design constraint:
The three little gas rings can be replaced with just one larger ring. The cam pin could be eliminated as a separate piece and merely be a protrusion on the bolt itself (eliminating the thin walls of the bolt). The 7 small locking lugs with space for the extractor means the lugs on either side of the extractor are under extra stress (and in fact are the ones that I've seen break). Fewer lugs would mean they could be stronger, evenly distributed (to compensate for the space taken by the extractor and distribute the force more evenly) at the cost of a slower cycle speed (cyclic speed is not a source of complaints that i have heard, and the AR doesn't really make use of anyway, except in the M231 version).
As mentioned previously, the forward assist, and the extra machine cuts on the carrier, are unnecessary. If someone really wanted to, you could just have a charging handle at the very front of the bolt, to tap to ensure it is in battery (which are available commercially), to replace the five parts of the forward assist with just one part (ultimately unnecessary).
If we don't limit ourselves to the gas tube/key/carrier design, then we end up with a piston gun, which doesn't have a gas key attached to the top with two screws, doesn't have to worry about a bolt-override malfunction, doesn't have any gas rings, has a different spring arrangement which doesn't need the buffer retaining pin (and it's spring) which I have seen break, and allows for an actual folding stock.
FOR ME, it comes down to this:
Why have the possibility of a brass over bolt (bolt override)?
Why have gas rings on a bolt (that need replacing eventually)?
Why have a bolt where the lugs can (and sometimes do) shear off, or a bolt that breaks at the hole for the cam pin?
Why can't I have a folding stock?
For what, cyclic speed I don't use? Light weight that doesn't translate into an appreciably lighter weapon (than a piston design)?
The only advantage I can see - inherent to the gas tube/key/carrier design - is less reciprocating mass for quicker follow up shots.
(Everything is irrespective of cartridge, as there are AR's, AK's, HK's, etc., available in different calibers like 5.56, 7.62x39, 7.62x51 etc. - so that is a separate discussion).
The ergonomics of the AK are terrible, except that I'm left-handed, so they actually work for me quite well, in fact. (It would be nice to have a bolt catch, admittedly, but I've seen people fiddling with their BAD levers, too.)
I'm not saying the AR is a bad rifle. It's just not for me.