Elias has played in 211 more games so far...that's more than two and a half seasons' worth, and that's a significant edge (definitely not "about the same amount of games", to be fair). For their careers, Elias averaged 0.827 PPG, and Marchand is at 0.903 PPG. Like I said before, for the balance of their careers Marchand's played on better teams, but over Marchand's last 575 GP alone he's averaged 1.113 PPG. Elias does not have a stretch like that at any point in his career, so I'd have to consider Marchand the more productive player overall based on these numbers.
BUT
If you want to look at a "career within a career", Elias did put together a stretch somewhat similar to what Marchand's entire career has been. From 1999-00 to 2013-14, Elias played in 989 games and put up 356 goals, 535 assists and 891 points...basically 30 G and 44 A per 82 GP...for this stretch he's put up 0.901 PPG. For Marchand's career, so far he's put up 32 G and 42 A per 82 GP, with a slightly higher PPG (the aforementioned 0.903). Like Marchand, Patrik's overall PPG average was hurt by development years; unlike Marchand, Patrik's PPG average was also hurt by decline years. We haven't seen those full-on decline years from Marchand just yet, and of course when we do, who knows when he decides to call it quits. He's only signed through the end of next season, and will be entering his Age 37 season when that contract expires.
It will be interesting to see how Marchand declines, to see if he can reach 1000 points, and to see if he decides to keep playing beyond 2024-25.
One last note about Marchand...he really found another gear offensively over the latter half of his career...insanely so. In his first 6 full seasons, he averaged 0.664 PPG (16:38 TOI per game)...over the next 6 seasons, it was 1.204 PPG (19:25 avg TOI). Over the past two seasons, it's been 0.865 PPG in 18:50 avg TOI, so maybe he is starting to slow up. But in those six "peak" seasons, Marchand's PPG was higher than Elias' best single season (1.17, set in 2000-01).