Well, I only have 16" barrels, so I can't comment on most of the questions.
You're correct in your two dealers, oustanding personal service and if you need something, no quicker than RA and a better chance of better communication as far as what's going on.
I think you're correct in your assesment of Robinson Arms and their past history. I also think that if people had "hiccups" with the rifle in the past, they were quick to give up on it for various reasons.
On a whim some years ago picked up a used XCR on AR15.com, and fell in love with the platform. I have enough spare parts and have since picked up a few more leaving the AR platform.
Everyone who has come over to shoot and used my XCR really seems to like the ergonomics over what they have. Price point aint cheap though and I think most people are afraid to spend that kind of coin on a "unknown". No gun is perfect, but if you have problems and stick with it and figure it out, I don't think you'll find a more reliable rifle on the market.
I know I picked up a rifle from a forum member here that had nothing but problems with his rifle and sent it back to RA. When he got it back from RA he sold it. That gun has had over 2,000 rounds of very dirty cheap russian ammo with never being cleaned and has never had a failure in my possesion.