You can't compare like that. You have to be very deliberate when boxing in MMA, since otherwise you get taken down. You can't smother your opponent in combinations as you can in regular boxing. And that also affects your punch out-put. Penn is the best boxer I've seen in MMA, even if it was impressive to see GSP matching him in this department. But his technique is very good, below a world class level in boxing, but not by a terrible margin.
It's amazing that BJ is known for his incredible (on an mma standard) boxing skills, yet he got into MMA through BJJ. People seem to look past that while he is the best boxer in the LW division, he is also by far the best grappler as well. If he is beating you on the feet, then your ****ed because your not gonna win a ground war with him either. Unless your much bigger and stronger and equally as skilled (GSP) ....or unless he gasses.
It's a crying shame. His cardio looked a touch better but to build that resevoir he'll have to not get fat and keep training hard for the next fight.
True, Penn can take a great shot, has decent boxing & quite heavy hands, thats why he fairs well the majority of his time when standing but he aint no boxer in the real sense of the word, his best strengths are his world class BJJ & his takedown defence IMO. Penn possibly has the best BJJ of any elite MMA fighter & its that skill more than any other that has cemented his place in any sane persons mind as the GOAT at 155 lbs & very near the top in a p4p sense.
BJ Penn punches like Bazooka Limon if you know what I mean. He doesn't dance and jab - but his punches are solid.