I'm not saying it a failure to build and own. Or that or can't be done

Example-
Getting a 6.5 creed chambered ar10 to cycle right makes for an amazing range toy.
(There's a reason i keep several adjustable bleed-off gas blocks on hand)

I'm addressing the claim of "ultimate". 

They are almost always much more finicky and issue prone and it wouldn't be my first choice in a complex situation.