Marchand and Marner? I mean, did you even look at the details of this before saying anything... it's not even close.
Marchand had been in the league for six full seasons when he signed his deal, with a career high of 61 points, and a second best season of 55 points. He signed a deal worth 8.39% of the cap.
Marchand is more comparable to Nylander at the time of the contract signing, though even Nylander had outperformed Marchand at that point, and he signed for 8.76%
Marner had a 94 point season before signing... attempting to compare that to a 61 point season as a best after six years is ridiculous to be honest.... I mean, Boston got extremely lucky that Marchand somehow just kept on getting better, but that isn't the norm.
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Bergeron signed for 10.69% of the cap, after having averaged 32 points a season, for the prior six seasons. He missed a lot of time over that period, but still... his best season during that stretch was a 64 point season and 22 goals. Yes, he'd had that 73 point, 31 goal season, but that was SEVEN years in the rear view mirror.
Meanwhile, Matthews was PPG, and had put up 40 goals.
These just aren't comparable... or even close. Boston got extremely luck with when they had to renogotiate their contracts. Our guys broke out before extending... theirs after.