BJ has had a very odd and unique career.
Even in his prime he lost a lot of fights because of his poor cardio and his insistence on fighting above his weight class.
If you look at his lightweight title defenses, they're honestly not that impressive. Sherk, Sanchez, and Florian were all in that journeyman-gatekeeeper range. But then again he did choke out Hughes and take GSP to a split decision.
I think in the modern MMA landscape a guy like him couldn't get away with fighting so high above his weight class. If he had come along around this time he would have had to spend his entire career at featherweight to be successful.
But you have to give him props for doing what he did. How many times did GSP fight at middleweight in the UFC? 0. BJ's legacy was never about having a pristine record. It was about fighting anybody at any weight and always looking for the finish. He had violent, entertaining fights. Not sparring sessions.