Sure, GSP has got more credentials.
But the P4P is also about who seems like the most dangerous guy to fight at the moment.
I would not hold GSP as the favourite against most top 3 middleweights or welterweights right now, but I would hold Conor as the favourite against anyone in LW or FW except Khabib.
Two points:
Thats not a fair comparison. Conor is a Natural LW. He can't make FW anymore because they took away the things he relied on to make that weight to fight much smaller men. He himself called them midgets.
GSP is a natural WW. So either compare GSP against WW & LW or compare Conor vs LW & WW.
The point of P4P is theoretically if you were to magically correct for size who is better.
If you could make GSP 185 lbs without any cutting weight aka walk around weight and did the same for Conor who would win? If you answer Conor you are delusional. Conor has never faced an opponent outside his own weight class. Nate Diaz is a LW. Just becasue Nate and Conor didn't cut and fought at WW doesn't make them WWs. KJ Noons and Sam Stout were scheduled to fight at LW and the week of the fight they both agreed to skip the dehydration to hit 155 and moved their fight up to WW. That doesn't make them true WWs.
The point of P4P is completely subjective however there is more evidence for some fighters then others.
DJ fought 13 fights at BW despite being a natural FlyW and he fought 16 times at BW and won 14 with 2 decision losses both top 5 fighters and one of them was champion.
DC fought 13 times as a HW and was undefeated before moving to LHW where he has proven to be the GOAT LHW this side of Jon Jones.
GSP had 9 title defenses in a row against every different type of skill set and beat them all. Many were accomplished MWs: Jake Shields, Frank Trigg and he was so dominant they were not even close most of the time. He also beat the Reigning MW champion Mike Bisping.
Conor was 1-1 with Nate Diaz who is a LW with a 19-11 record overall and has a short stint at WW going 2-2. He had 16 LW fights before that and 8 LW fights after that with 2 WW? bouts against Conor. Conor has never fought anyone from a bigger weight class and the biggest fighter he fought is a journeyman that he lost to.
See the way that you can objectively assess facts to come up with an opinion on a subjective thing like P4P.
Based on the above would you rank Conor ahead of any of the other 3?