Oh really? Let me name some who don't belong in that list:
Garner
Croft
Donald
Nawaz
Imran Khan (Wasim and Waqar are better bowlers)
Ambrose
Holding
He did face better bowlers than those^
He also played on pitches if when used now would be called underprepared and deemed unproper for international level, had hardly any padding (So he was almost literally playing for his life), and at a time when Bodyline was the norm. Also, he had more strain on his body, travelling by ship to and forth is tiring enough. But he also didn't have any professional physicians around to help keep him in shape (And yet he played to his mid-forties).
Also, they weren't as tough on chucking as now, and the balls used to seam and swing more (not so sure about that). So he could be facing bowlers who chucked quicker than Akhtar without a helmet on a deadly pitch with the ball swinging like a bannana. And he averaged 99.94.
He also didn't have the comfort of minnows.