What kind of "man's man" initially complains about having to go on a hunting trip, then protects his fancy watch and sits at the table while his brother and 70 year-old father battle it out with a group of men who attacked them physically? The mug smash came after Jock and Bobby and Ray did the real work - it was cute, but superfluous. Bobby and Ray rightfully tease him for it on the way out of the saloon.
Then JR has the mosquito net and full cot when they're camping in the woods as the others just sleep on the ground - an instance of the writers shouting out "this is a prissy wimp".
Interestingly, though, when it came down to it, as with the life-or-death struggles with Ray and Nicholas Pierce (and when he slapped the dastardly Jeb Ames upside the head when he threatened Bobby), if he absolutely had to, JR actually could handle himself physically better than we were led to believe over the years. He also showed courage staying behind with a wounded Jock and a shotgun, when wounded himself (although he ended up falling asleep and letting down his guard). He had some of Jock's physical toughness after all!
Very interesting analysis, Guzzler! You definitely showed yet another perspective, which is what happens when the forum is at its best - we get a bunch of different perspectives. There's not much that's worse than a forum where everyone (like on the opening to King Of The Hill) just says: "Yup, yeah, yup."
My take on it is that: Bobby and Ray are naturally more athletic than JR for one thing. That's a big thing. Anyone who has played sports knows that if you don't have a certain amount of innate talent for athletics (including fighting) such as hand eye coordination, reflexes, speed and strength then no amount practice will make you great or even good.
Also, while Bobby was playing college football and Ray was being a cowboy, JR was working a desk job, so there is no reason he should be in their physical condition.
JR could and did rise to the occasion when he had to, like when he fought Nicholas Pearce, or even having the guts to tell Bobby and Ray to both go for help(when it would have been safer for him he asked only one to go) during Dove Hunt.
People have different areas in which they excel and JR concentrated on business because that was where he excelled. JR couldn't do what Ray could do but Ray couldn't do what JR could do. Bobby had the most overall gifts of all three brothers, but maybe the least dedication to focusing on developing in any specific one of them because he kept jumping from one career path to the next.