With Bushmaster, Remington, DPMS and God knows who all else now falling under the aegis of Cerebus, I think some of the suppliers are the same. I've got an upper built by J&T Distributing. It's Cerro forge marked, as are many of the RR and Remington ARs I've seen.
For pins and springs, even the sub-80% forging, I’d agree.
However, Bushy and Remington make/assembles their own uppers, because that is where all the work is done and that’s where the quality or lack thereof becomes apparent.
Interesting to see that Remington has taken the former Masada/MagPul ACR and made it their own. Given Remington’s work with the M24 weapons system, it might show quite favorably as a tactical rifle than it would under the Bushy lineup.