I think your post has some merit and I agree with some of the points. My military experience was mainly with A1's and 5.56, so my opinion is biased. The main reason I've stuck with .223/5.56 as a civilian is pretty simple: cost. Now that Uncle Sam isn't supplying me with ammo I've found that I can shoot more for the same money with 5.56, and at this stage of my life that's very important.
I was impressed with what the M60 could do though - what's considered cover against 5.56 is sometimes only concealment to the 7.62 round...
In a real SHTF situation you should probably be escaping and evading instead of trying to use supressive fires, but that's just me.