He was a teenager when he lost to Maxim, wasn't even fully delevoped. And he had a hiccup against Inge, something that happened to most of the HW champions. He then came back to smash him twice in 2 great fights.
In all fairness to Patterson, most accounts say that he was the winner. I have never seen the fight (not sure if it is even extant) and I don't know how bad a screwjob it was.
What about WBO champ Francesco Damiani? Former title contender Francesco Pianeta? Hell, they are probably the two best Francescos to ever fight at heavyweight.
Technically, it's no more incorrect to say that Messi was one of the top 5 most underrated heavyweights.