This basically illustrates the need for a tight, repeatable lock up between an upper and a lower... which many say is not important.
Can't agree with that statement. You are comparing apples to oranges, IMHO.
A standard rifle has the barrel/action attached to the stock....and so the action screw torque plays is important. The fit between the barrel and stock is equally important. Anything loose there will put you all over the target.
On an AR platform, the barrel is attached to the upper receiver. So it is important to have those two properly torqued. The barrel does not interface with the lower receiver and so the fit between the upper and lower makes no difference. I agree that a sloppy fit is annoying...I don't like it and won't put up with it. But it is not an accuracy issue like a loose barrel in the upper receiver would be.