I'll post this here, since it's (predictably) turned into another Crosby vs McDavid debate. I'll compare both players' output, relative to the top ten scorers in the league. (This is done in order to reflect the reality that McDavid has, on average, played in a higher-scoring environment than Crosby).
In terms of what the numbers mean - for example, in 2023, the top ten scorers produced 1,147 points. McDavid scored 153. His result is 153 / 114.7 = 1.33.
Comparison of points by age
Commentary: Crosby has a big head start. He had a very good season at age 18, and an even better one at age 19 (McDavid missed nearly half his rookie season). McDavid has three blowout wins (ages 20, 23 and especially 24 - Crosby fans will be sure to remind you that these were the years where he missed a lot of games). There are six close calls, where they finish within +/-9% of each other (McDavid is ahead ages 21, 25, 26 and 27, while Crosby is ahead ages 22 and 28).
Comparison of points (best to worst)
Commentary: this is showing their results, sorted from best to worst. (In McDavid's case, this is his entire career; in Crosby's, it also includes campaigns from the second half of his career). This is fairly one-sided in favour of McDavid. If we compare their best full seasons head to head (2014 and 2007 vs 2021 and 2023), McDavid is clearly ahead. When we compare their next six seasons (ie their 3rd through 8th best seasons overall), McDavid is ahead each year, but it's closer. It's remarkably consistent - he's ahead 5-7% each season. The 9th best season is a tie, and Crosby is only ahead when we look at their 10th best seasons (Crosby's 2019 campaign vs McDavid's injury-shortened rookie year).
Comparison of PPG by age
Commentary: Crosby has three decisive wins (>10%) - ages 19, 23 and 25. McDavid has two decisive wins - ages 26 and 27. All the other years are fairly close.
Comparison of PPG (best to worst)
Commentary: in all ten years, they're within +/-10% of each other. In fact, in nine of these seasons, they're within +/-5%. Crosby is slightly ahead overall (he leads in six of the ten categories, and he's ahead by 2% across the entire period). I was surprised to see that Crosby is ahead in all five of their best seasons head to head.
Overall, if we're comparing actual output, McDavid is unquestionably ahead through ten seasons. The comparison is a bit closer than it looks at first (because McDavid has played in a higher-scoring environment), but there's no question that he's ahead. If you think that PPG is a better measure of a player's ability, it's very close, and in fact an argument can be made that Crosby is slightly ahead. I think it's plausible to argue that both centres have similar ability.
There are a few important disclaimers. First, these tables are taking their pace (i.e. points per game) at face value. McDavid has been much healthier, so there isn't much question as to whether his numbers are sustainable. That's not the case for Crosby (ie would he really maintain a pace of 1.68 PPG over 60 extra games in 2012, when he never scored at that pace in any full season?) Second, this is assuming that both peer groups are equally good. I think people tend to exaggerate the gap, but on balance, McDavid has probably faced tougher competition (though not by much). Third, Crosby has a reputation for being a better two-way player, and that's not reflected anywhere in these numbers (which are solely about point production).