This is simply a semantic disagreement. I dont think McDavid is as good as Lemieux but I have them in the same tier of all time generational superstars. Like the best of their generation. Lemieux was just strictly better, but they both are in that tier. You can define tier however you want though.
If you define tier as the player has to be the same level where any discussion between 2 players of that tier is a 50/50 toss-up then I wouldn't put them in the same tier.
It probably doesn't matter because Jagr didn't exactly compete against Lemieux for scoring titles, if he did, he never really beat him.
Jagr won the scoring title 5 times.....4 of those seasons Mario didn't even play and the 5th he only played 43 games. If you want to look at the other years that Jagr didn't win the title anyway....go through every year of his career up to when Mario retired
1991 - Mario played 26 games
1992 - Mario outscored him
1993 - Mario outscored him
1994 - Mario played 22 games
1995 - Mario DID NOT PLAY
1996 - Mario outscored him
1997 - Mario outscored him
1998 - Mario DID NOT PLAY
1999 - Mario DID NOT PLAY
2000 - Mario DID NOT PLAY
2001 - Mario played 43 games
2002 - Mario played 24 games
2003 - Mario outscored him, even though he only played 67 games
2004 - Mario played 10 games
2006 - Mario played 26 games
And yes, I get showing that Mario outscored him shows that he "was competing against Mario for titles" but that wasn't really the case those years as it wasn't like he was finishing 2nd in scoring in years where Mario was winning....that did happen once in 1996 and that's where some start talking about whether he would have scored that much without Lemieux, etc....you can argue either way there....but the point was that it's a bit of an exaggeration to say Jagr had to compete against Lemieux, so his wins are better.