That's because the simplest efficiency ratings like PER favor scoring above all else. Scoring rebounders tend to yield the most inflated PER above their actual skill/impact on the game; so workhorse double-double players like Boozer tend to be the most overvalued by PER. However, IMO, I've always loved PER for highlighting this group because there is no group of players that is as chronically underappreciated and undervalued by casual fans who have never played organized competitive basketball. Bad rebounding, poor shooting, and turnovers lose games. Period. The Carlos Boozer's and Elton Brand's of the world never get their due. Thank God David Lee finally got some All-Star props this year. The greatest player who isn't afforded his due respect in the grand scheme of the basketball canon who is redeemed by the PER is Kevin Garnett.
A few more objections to your point:
(1) Comparing career PER's of inactive players (Pippen, Russell) to an active guy whose numbers aren't diminished by the inferior production of his later years is flawed.
(2) Jason Kidd shoots poorly and outside of his peak years never contributed much more than 10ppg. The PER reflects this. It's a sobering reminder that excellence in one thing doesn't equal excellence in all things.
(3) Russell was a defensive specialist, and this group is easily the most undervalued by PER. Furthermore, they didn't count blocks or steals during his career, so he's an incontrovertibly inadmissible example to contrast to Boozer. Some of the older analysts who watched games courtside during Russell's prime estimate that he might have averaged as many as 10-15 blocks per game. Counting numbers like that he unquestionably would have surpassed Boozer, and that's with the crippling disadvantage of defensive specialism (for which traditional stats don't reflect true performance).
Kobe is a scorer, and an above average rebounder (especially for a guard who also tend to get more assists, steals, and shoot a higher FT% that bolster their PER). Unlike the defensive specialists of the world, he has no real gripe with the PER that has LeBron shitting all over him.
