
I think winning percentage can be a pretty interesting stat, especially if you're looking at a player who's purported to be the best player on the team. It says a lot, to me, if your best player can't lead your team to a .500 record. Especially if that's the case for more than one season.
I'd like to hear exactly what you think it says about a player, since it pertains to players like Ray, PP and KG. They're all in the "more than one season" category, so explain that group in particular.
I don't know if it says one thing about all players across the board -- that was the Kyrie/Love example: Irving gets more leeway from me because it's still only his third year in the league. I pay the most attention to it when it becomes a trend: Love is a good example of that because he's
only had losing seasons since he's been in the league. But there are different factors at play there -- Kevin Love's Timberwolves being perpetually bad may not be for the same reasons as Irving's Cavs.
You need to add Deron Williams, Ray Allen, Dwayne Wade, Kobe Bryant, Paul Pierce, Carmelo Anthony, LaMarcus Aldridge, and Kevin Garnett to your list of players who have had seasons in their primes where they have led their teams to sub .500 records.
I'm sure there are some other notables who I've missed.
There's a difference between being the best player on a team that's had one or two losing seasons and being the best player on a perpetual losing team That's the nuance your list is missing. So KG was on losing teams for the first two years of his NBA career -- and then his last two years in Minnesota, with eight seasons of high level play in between (Not to mention an MVP award).
So what does that say about Garnett? That he's a guy who needed quality teammates, but could still be the alpha dog on a 55 win team. Aldridge's career so far has been similar.
Carmelo Anthony has only had one losing season -- this year, and you can look at the data any way you want and see that it largely wasn't on him, he played his ass off. Again, aberration against a ten-year professional career.
Wade's injury history has to be taken into account when you look at the seasons the pre-lebron heat had, etc.
And so on and so on. You can't just lump them all into a pot and say "losing seasons."