My "slight nod to RRA" comes from the fact that RRA has more factory choices, you can get a stainless bbl. if desired, and at least in my area, RRA has a little better resale value than Stag should you decide to move it for something else. Absolutely nothing wrong with Stag in my eyes.
DPMS has great lowers to build on, but that is about as far as I would go with them. I don't think they are horrible, but they seem to have their own "standard" on many of their parts.
After owning some Oly Arms rifles, I can honestly say I wouldn't suggest them either.
As far as being "just assemblers", Colt doesn't make much in house either, yet they seem to be sort of a grail to many.
It's all about the end result...best features, quality, value for your buck. I will not pay the going price for a Colt. I like Bushy rifles, but when I can get a chrome lined Stag or RRA cheaper, that will suit my needs just fine. I don't really feel you can go wrong with most of the choices out there. I have a J&T kit on a stripped Superior lower with a RRA lower parts kit, a factory Bushy upper on a stripped DPMS lower with a RRA lower parts kit, and a Stag complete upper on a complete RRA lower. Not had a problem out of any of them, and they were all done cheaper than buying a factory built rifle.
If and when I get around to building another rifle, I will most likely go with Stag, or RRA, or a mix of both again.
There is my opinion, and its worth what you paid for it.
Buy, shoot, enjoy, rinse...repeat.