DOD cheaped out on ammo or some shit, the m16 could have done better for the imperialists at the time without changing the gun, but they fucked up.

today the ar-15 derivatives are probably better for most purposes because they take optics better and polymer is good and light, which you want because you're carrying your gun way more often than you're shooting it. If you're a nation-state fielding an army there might be supply chain considerations that would put you on AK derivatives instead.

for civilians you probably don't need a gun, and if you do need a gun you either need ten friends with guns too and matching your friends for spare parts and sharing ammo matters more than the platform, or you're hunting and you aren't terribly likely to want an ar-15 or ak at all.

bombs are probably better than guns but leftist violence would just be used as an excuse to crack down on everything so, you know, probably don't do any of that.