... you can build an AR platform that is equal to a bolt action rifle in accuracy easily enough.
Well, to a point. For most practical applications I would say I agree, but ultimate accuracy at long range is still a single-shot bolt action.
I have a couple Rock River ARs that are pretty darn accurate. A National Match AR-15 and their LAR-8. I do not handload and the NM is a sub MOA rifle at 200 yards with factory ammo. I have not shot the LAR-8 enough yet to know, but it's close.
When you get to 800+ yards and need to stay supersonic to the target a 20", or even 24" barrel isn't going to do it. Now if someone made a .338 Lapua or .416 Barrett, or .50 BMG AR that may be a different story.
The F-Class guys I know are running 30" +/- barrel .308 Win. Of course, custom, hand loaded ammunition. 5" X-ring and 10" 10-ring at 1000 yards.
Generally speaking, my experience is that beyond a relatively easy to attain hardware aspect, practical accuracy is more a factor of the rifleman than the rifle.
Again, agreed, to a point. Are we talking about bragging rights at the deer camp, or on a firing line at a regional or national match?
That "relatively easy to attain hardware" will run you on the order of $5000 and up for a rifle (no scope, no rest). Guys are paying more for their rest than most folks spend on a rifle and scope.
Guys are so good that regardless of skill, you will not consistently "win" a match against the top-flight competitors with a $2000 rifle.
I do not compete at these levels, but I shoot with guys that do.