first off, no offense but in threads like these there's no point in listening to anybody with a 2014 and newer join date, lol. Sorry to lump some of the old school lurkers with them, but there's too many Conor nuthuggers that partake in these discussions while their only knowledge of Penn is watching old highlights and seeing current BJ get embarrassed. It's easy to discredit the names on his win list when many of them are at or toward the end of their careers, when losses are not uncommon. Defeating Matt Hughes at WW for the belt was easily as incredible an achievement as Conor defeating Eddie. New fans don't understand that context because Hughes has no aura anymore, but he was one of the P4P best at the time, and remains a top 10 all-time fighter.
secondly, prime BJ doesn't fight anything like the guys Conor has been wrecking. McGregor has an amazing left hand, great confidence and is the most entertaining on the mic, but BJ would have made it a grappling match, and had the granite chin, boxing talent, and most importantly, the poise to make it happen. BJ can survive McGregor's world, but Conor has never showed us anything to make us believe he could stop Penn from slicing through his guard, taking the back w/ hooks for an RNC. He'd probably trap an arm while he was at it.
In all honesty I kinda feel bad for the folks that missed out on prime Penn. He was a beast. And for the old school guys that still think Conor would murk BJ, power to you. McGregor has a monster left hand (most accurate/powerful punch in the history of the lighter weight divisions imo) and these threads are obviously just conjecture. Cheers.