Basketball does have stats that measure relative performance across eras — none are perfect, obviously, and many under-rate defensive value, especially when you consider blocks/steals have only been a tracked stat since 1973/74. Additionally, they are really a poor measure of overall defensive value.
As stated win shares are a one way to measure a player's total career value, but are heavily influenced by longevity. You can take some of the longevity bias out by looking at win shares per 48 minutes for example.
That list would look like:
1. Nikola Jokić .2541
2. Michael Jordan* .2505
3. David Robinson* .2502
4. Wilt Chamberlain* .2480
5. Neil Johnston* .2413
If you want an efficiency based stat that is adjusted for season-to-season game pace and annually adjusted to have an average of 15.0 you can look at PER. This pace adjustment allows for better cross-era comparisons, though earlier players will loose credit for the lack of recorded blocks/steals. It also does not incorporate team success, or lack thereof in any way.
1. Nikola Jokić 28.08
2. Michael Jordan* 27.91
3. LeBron James 27.06
4. Anthony Davis 26.84
5. Shaquille O'Neal* 26.43
BPM (Box Plus/Minus) is another rate based stat you could consider or VORP (Value Over Replacement Player) is a cumulative stat — though neither use data before the aforementioned 73-74 season.
You will note rate-based stats tend to favour active players — they are yet to complete the "down" phase of their career — while cumulative favour retired as they have had their whole career to accumulated total stats.
All-in-all, as mentioned in the poll posts, there are lost of ways to skin the proverbial cat and no right or wrong answers. Anyone, who thinks they have one is delusional, but it's a fun conversation.
Irrelevant to the "GOAT" conversation but in reference to cross-era discussion:
I started playing around with regression analysis to examine the stats that had the most effect on whether a player was named to the Hall of Fame with the aim of building my own stat similar to the Hall of Fame Monitor score from baseball. Unfortunately, changing life circumstances have put that on hold.
I do still much around a bit with cross-era box-score stat comparisons via normalising the stats to a single year. This is nothing technical but does throw up some interesting and sometimes unexpected results.
For example Chamberlain's 27+ rebound per game seasons are not close to the best rebounding seasons ever when normalised to the number of rebounds available. Dennis Rodman's 18+ rebound seasons in 1991-92 and 1992-93 come out easily tops and his next two seasons are third and fourth. (This is even without normalising for Chamberlain's super-human minutes per game numbers.)
In a like manner Chamberlain's 100 point game — in a season when team's averaged 118.8ppg — grades out as being less than 1ppg more impressive than Kobe Bryant's 81 point effort in 2005-06 when team scoring was 97ppg. Both narrowly edge Joe Fulks who put up 63 points in 1949 when the average team scoring was only 80ppg.
