JW is a gunslinger and a brawler whose drive for the mission is relentless because emotions, rage, and anger lead him. As such, he is prone and open to making careless mistakes as he does not meticulously think through dangerous situations. His stubbornness is what fuels his victories. On the other hand, when you look at RM, he is a thinker who can take out an entire room based on critical situational analysis of what can be used to secure his victory. He is the ghost that kills you without you knowing he was there, and even if you do, you're too slow to react to it. JW has yet to demonstrate this ability. Also, let's consider the ages of both of these killers. JW is five years into retirement and, by all metrics, still is very much someone who can jump back into the game at will (as proven by the movie). Now, when you consider JW, he is basically into his senior retirement age with quickness and precision rivaling most opponents he faces. Imagine if he was 25 years younger. The speed at which he can kill is exceedingly more incredible and efficient. Hence the reason he times himself and is slightly disappointed that his killing time is increasing with each passing kill. To me, this communicates that this man was once untouchable. JW has never taken out a room without his gun. RM has done it multiple times.
My dos pesos.