You can't rank Aoki higher than he is. Barnett and Vinny are both recent world champions in nogi, Palhares came 2nd at Abu Dhabi to one of the best on the planet in Galvao and only lost by close decision.
Aoki gets murdered by anyone with the ability of the guys in the tier above.
Arona and Monson are hovering between tier 1 and 2 because they aren't as good anymore, they were up with the best in their day though.
Filho is comparable to a Nog, above the 3rd tier but not quite the 2nd tier. (probably not anymore but during their primes that was where they would be)