I'm not a fan of picking apart records like this. You can go through any fighter's record and start discrediting wins, and it's really not fair to great fighters to go back and nitpick records. Penn earned himself a number of enemies with his behavior after UFC 94, and those enemies want to discredit everything he's done in MMA. I'm sure if Penn beats Florian his detractors will claim Florian was never that good anyway, but a win over Florian effectively secures his spot as the best lightweight in the world.
This won't be an easy fight for Penn. He has better boxing, wrestling, and jiu-jitsu than Florian, but Florian has better cardio and a number of weapons from range he can use to effectively nullify Penn's advantages. Florian has become an evasive counter striker on his feet; I expect him to make BJ chase him and try to catch BJ with body kicks when he closes in. The key for Penn in this fight is to resist the urge to fight standing and get Florian down. Penn's offensive wrestling is underrated; he definitely has the ability to put Florian on his back, and that's where Penn can really do a lot of damage.
From my perspective, Penn's legacy in the sport is secure. But a loss to Florian at this point will give a lot of ammunition to those who have long believed he has never lived up to the hype.