As a starting PF, he's probably the 20-30th best in the league, which is considerably below average. As a first PF off the bench, he'd be a top 5 in the league.
Where'd you get that?
http://www.fantasysmacktalk.com/2012-2013-fantasy-basketball-power-forward-pf-rankings/
This is fantasy basketball so obviously players who put up empty numbers are favored.
But outside of the top 10, 15, it's a tossup.
Who's better between Glen Davis, old Boozer, Bargnani and Humphries? You can't really say. BBD is kind of a headcase who doesn't really board. Bargnani is soft and doesn't play D. Boozer doesn't play D at all.
Rankings are kind of completely crap like that. Top 10 lists...ugh. ESPN bullcrap. It's just easy journalism, especially when they make lists without numbers. Tiers of players makes a little more sense.
Plus Hump might be playing the 5 anyway. If he does what J.J. Hickson did, like IndeedProceed is saying, I'd be happy. If he played a little D.
Of the guys you said, I'd rank them as: 1. Boozer 2. Bargnani 3. Humphries 4. Davis
So there's 2 that are better than him... Then lets go with Duncan, KG, Bosh, Faried, Dirk, Kevin Love, Pau, Z-Bo, Josh Smith, David Lee, Blake Griffin, Milsap, Aldridge, David West, Ryan Anderson, Anthony Davis, Amare who are all pretty clearly better than him. Then he's somewhere in the class with players like Bass, Carl Landry, Tristan Thompson, Taj Gibson, Amir Johnson, Sullinger.
This list isn't perfect but I don't feel like spending a lot of time on it. The point is that there are a LOT of PFs better than Humphries.