I mean, it's tough to argue that Kawhi (when healthy)
has been the better player over the past 4-5 years, but again, I think people tend to underplay how much better it is to be 27 than 34 in the NBA. By way of comparison: I think it's unrealistic to expect Jason Tatum to be as good as peak Kawhi this year, or even next year, but I think by age 27 he's a pretty good bet to be better than Kawhi at age 34 (assuming reasonable health all around).
One could argue that LeBron's anomalous since his boxscore numbers at age 33 showed no decline. He obviously pays fanatical attention to his body, has ridiculous genes, and probably has excellent pharmacists to boot, all of which will no doubt help in his efforts to ward off Father Time. But it's worth noting that his advanced stats last year
did actually indicate decline. By RPM, he slipped to #12, and that number is buoyed significantly by RPM's generous boxscore correction. His on-court impact last year in terms of wins and losses was shockingly meh by his lofty career standards. Put simply, he just played an entire 82 games season plus 22 playoff games in which
his team was not substantially better than the opposing team when he was on the floor (+1.6 points per 100 possessions better than the opponent in the regular season, -1.1 points worse in the playoffs).
We can certainly blame his crap teammates for a lot of of that, but I think it's also reasonable to surmise that at age 33 his defense (half the game) has fallen off significantly, and will continue to do so as he enters his mid-30s.
Also, this: