Shooter,
I think we are closer in opinion than it would appear. However, the failures of the M4 in the battles at Shah-i-kot, and more importantly, at Wanat, were not due to problems inherent with the DI system. They were failures to adhere to the firing schedule. Not that they had a choice under the circumstances.
Like I said before, the HK416 and M4 share the same max sustained rate of fire. The failure point is the barrel, not the gas system. Even the M27 only increases the Max Sustained ROF to 36 rounds per minute, which is about 1/3rd that of the weapon it is replacing; the M249 SAW. A decision I personally think is a mistake, but who am I?
Now, do we have a relatively close comparison of how the regular length barreled piston, 5.56 weapons have done? Kind of, check out some stories on the feedback for the HK G36 in theater. Once again, the barrel is the stumbling block.
As to the SCAR FOW...
It is my first choice for a sub 11.5 gun that will be suppressed. In that role it shines. If I were to use a rifle that had a longer barrel; in 5.56, I would have no problem with a quality DI system. It has everything to do with dwell and unlock time. I believe the 416's used by the Unit are 10.4 in barrels as well.
Yes, SOCOM uses the SCAR system. That program just received a 5 year extension. In the Mk17 configuration with conversion kits for 5.56. There are some Mk16's in inventory, but only at one location that I am aware of and all of them are CQC models. Currently there is one company working with SOCOM to field conversion kits in other calibers as well, including 7.62x39.
In short, I think the piston 5.56 platform has it's place, under certain circumstances,( I love me some SIG 552...) but outside of those the differences in reliability are minimal and come at the expense of other potential failure modes.
EDIT: to add underlined info.
Everything you said is valid EXCEPT if you figure SHTF...not a short SHTF scenario like the downed helo, but 3yrs n the bush with no gun oil...if I had to pick what rifle to have under that condition, it would not be a DI weapon...that is the jist of my point. But if you are talking consistent fire in a long firefight, the barrel would be a weak point. You are very well informed and I respect your observations. My point is very specific I guess..."worst case scenario Mad Max post-apocalyptic conditions".