I have been a bolt guy for 50 years and bought an R-15 three of four years ago for coyote hunting. I, too, have some trouble using the AR in the field. I think the reason is that my 'muscle memory' is so 'set up' for traditional style stocks that the transition to an AR is really rough. It is different, and the difference is significant. As you note, target shooting is not a problem. But quick field shooting is.
At this point, I switch back and forth between my bolt .223 and my AR. I do as well, or better, with the bolt gun. I really thought the AR would improve my kill rate. I never would have thought that I could do better on a running yote with a six-shot bolt action than with a fully loaded AR. But, I can.
I bet some of these younger folks who have shot nothing but AR style rifles have the same problem in reverse. Of interest (at least to me) that when the Army got me in 1971, I had already been shooting for years. Some of this shooting was competetive. The M16 drove me crazy! Especially 'night fire' where you had to shoot instictively. Even then, my muscle memory had an adverse effect on my AR style rifle performance.
I am not getting rid of my R-15, and I still like taking it afield. Maybe someday the coyotes will wish I had brought the bolt gun. Never to old!