Right off rip, I don't particularly care for JBJ. I don't necessarily think he's the p4p greatest either. I honestly believe that if you could magically shorten his arms by six inches on both sides, he would get decimated within two fights. He has learned to master his physique....a strong/massive/long upper-body, (where most of his weight is) and his skinny little legs...which aren't energy expensive and he can swing around for various kicks with little effort.
His long arms keeps his opponent at bay to stop the incoming legs kicks (which would otherwise cripple him) and also makes it tougher to get takedowns...which is in my opinion the way to beat JBJ...flurry to the inside with punches and then land demoralizing leg kicks like Barboza followed by takedowns with GNP.