Is "PER" a Perfect Tool To Analyze the Greatness of NBA Players?

I saw a discussion today where the argument was made that kevin Johnson was a better player than Isiah Thomas because KJ had a better PER during his years in the league. 

So, I thought, I know Jordan and LeBron are ##1 and 2 overall in career PER, so is it really that accurate of a tool to judge player greatness?

Turns out.............no.  Guys with their all-time rank in PER:

6.  Dwyane Wade - great player, not the 6th best player of all-time.
7.  Chris Paul - same

10.  Neil Johnston* - quick, tell me who Neil Johnston is....

22.  Yao Ming -

25. Dwight Howard

26.  Amare Stoudemire - some would say he is not a top 26 player in th eleague right now.

27.  Tracy McGrady - 0 playoff series victories

30.  Pau Gasol - hey, Laker fans, is Gasol the 30th best player in the history of the game?

33.  Bob Lanier* - loved Buffalo Bob, not a top 33 player

34.   Clyde Lovellette*

36.  Adrian Dantley*

37.  Harry Gallatin* - I do not know who harry Gallatin is/was

 41.  Elton Brand
 48.  Chris Bosh

49.   John Drew -  really, John Drew?  top 50 all-time?  This astounds me.