Exactly as expected, most people do not like the eye test because they either have to say someone isn't as bad as they thought or players often cited as the best are the same as the guy they don't like.
Bergeron, Stamkos, Tkachuk, Matthews.
The fun part of this exercise is that these are the closest forwards to each other in terms of P/G (50 games or more) but only two are are described as playoff duds, five of them would be described as the opposite. If we looked at numbers post-2000, a few other names show up in this group (.88 to .82). They include playoff duds like Brad Marchand, Henrik Zetterberg, Patrick Kane, Jonathan Toews, Jarome Iginla, and Marty St. Louis.
I think you really have to be free of bias when making this type of comparison. Its a titled comparison to look at guys playing past R1 vs leaf stars who onky have R1 career stats. Their 1 R2 we saw Marner with 3 in 5, Nylander with 3 in 5 and Matthews with 2 in 5.
Also The names you mentioned for post 2000 group, there is a lot missed when looking at superstars of an era where the stars put the numbers again over multiple rounds vs only R1, scoring was lower, goalies were better and you include age 35+/post prime years for career comparison for this group vs Marner(or a nylander/Matthews) all having been in their primes without their decline years in mid 30s included in their career averages.
Zetterberg --> has numbers over multiple deep playoff runs in lower scoring environment. His peak he won the cinn symthe and outside of that in his prime he was constantly a great 2-way 1C who could line match and put ppg up.
Toews & Kane --> have their numbers over 5 deep playoff runs in a tight checking WC in a low scoring environment. They both have a Conn Smythe and were two if the top 5/6 playoff performers in the NHL from 2006 to 2015
Marchand --> You include his numbers before he broke out to a superstar to get him into the cutoff. We have seen what Brad Marchand does first hand in 2018, 2019 and 2024. He was much much better than any leaf in all three of those series. He had 99 pts in 91 games from 2017 to 2024 playoffs (89 pts per 82)
Iginla --> he's the worst playoff performer of this group. He did play on the worst team, in a lot of DPE hockey (his whole career basically besides any runs in maybe 06 & 07 if flames made it) but still had a strong run in 04 where flames lost in 7 to the Bolts.
MSL --> won a cup + had another deep ECF run. His career numbers on Tampa (age 35 and prior) were ~89 pt per 82 player over 65 games. His age 38 and 39 playoffs drag his numbers down when he was a 3rd liner with the Rangers
Marner has put up hus numbers in R1 which is the easiest you get generally as you have more open stylef games, less worn out players on your teams, refs call more stuff in R1 vs deeper and your playing worse team in a R1 vs R3 or R4
Marner/Nylander/Matthews numbers all are really trash considering they put them up in R1 almost every time (1 2nd round run).
You would need to look at the current players playoffs by round and compare vs Leaf stars since those guys would have R2/R3/R4 (potentially depending on whose in there)