Sakurai is a tiny WW. If he was in the UFC he would be a LW. How can you compare GSP and Sakurai, thats nuts.
How can rank AOki #1, seriously? He lost at LW to Hansen in convincing fashion. Since going back down to LW, BJ has been unstoppable. Then you gotta go with the eye test, which fighter is better? BJ is better in every aspect of mma except fighting off his back, Aoki has a more dangerous guard. But BJ is the better LW and hasnt lost there in years. Aoki has gotten knocked out cold at LW then he fights a WW that isnt even ranked and gets KO's in 27 seconds. But sure, Aoki is the better fighter
His loss to Hansen is hardly proof positive of his skills. When was the last time Penn fought in a tournament and had to fight a fresh fighter after having winning a hard fought decision against a fighter like Caol Uno? That win has meaning of course, but not as much as you are leveling on it.
Also, your "eye test" doesn't mean anything in terms of rankings. For one, it is completely subjective. You definitely have an argument that Penn is more well rounded, but that isn't what the rankings are about. Plus, your opinion
that Penn would beat Aoki also means nothing. Aoki beat Eddie Alvarez who a lot of people were arguing would give Penn a run for his money.
All that truly matters are record and recent wins (including the quality of fighters those wins are over).
Aoki, like Penn, only has one loss against a LW and that is to Hansen at the end of a tough tourny. He also has wins over Cavalcante, Hansen, Caol Uno, and Eddie Alvarez. Penn has wins over Sherk, Joe (the perpetual Gatekeeper) Stevenson, and Jens Pulver (who is basically a declining FW).
Aoki's wins at LW are far more impressive than Penns. In fact, Penn's only really impressive win at LW was against Sherk.
The Sakurai fight, no matter what you want to argue due to Sakurai's size, has no bearing on the LW rankings because the fight was at WW. It means zip, squat, zilch, zero.