Quoting: DongLord23
Bergeron was not typical 1C money. Other 1Cs at the time.
Malkin 8x9.5M
Crosby 12x8.7M
Staal 7x8.25M
Getzlaf 8x8.25M
Stamkos 5x7.5M
....
Bergeron 8x6.875M
It was a huge discount compared to other top centers. Dude could've easily pushed for more than 8M a year.
Marchand was also a team friendly deal. He was 6th in goals and got 6.125M. His deal was similar to Kyle Okposo & Brandon Saad. He could've also pushed for way more.
I don't see Bergeron's deal as a huge discount compared to that list when you take it into context. That was Bergeron's 4th contract, and the list you mentioned was 2nd and 3rd contracts. Bergeron was older than any of those players were at the time of signing, meaning those 8 years were riskier. I think he could absolutely have pushed for more, but that's almost always true, and also would have been true for most of those players. Bergeron managed to age so much better than anyone could have expected given his early career injury history, and that is a huge part of that deal turning out to be such a massive value for the Bruins.
Marchand is a bit of a different animal. He again was older, that was his 4th contract, and his contract season was considered a bit of a breakout year, but he was still very underrated by the league (including the Bruins), so I am not sure he could have pushed the deal he got all that much higher. A 7 year deal from the open market would have been a higher AAV for sure, but I doubt he had the clout at that time to get much north of $7M unless he was willing to sign with just anyone. He was a better player than Okposo, but I don't think that was the consensus opinon back when he signed that deal, and again, it's hindsight that makes it look like he took some massive discount.
Marchand though was more of a case of a team finally realizing what they had. Marchand didn't just magically become an offensive force at 28. He was already putting up superstar level production, but his reputation as a shift disturber seemed to decrease the attention his ridiculous offensive skills should have garnered. The guy started putting up elite level scoring rates from his sophmore season onward. The totals just lagged the reality because he was getting less than 15 minutes a night, playing with 3rd line talent mostly and very little powerplay time. Even in his breakout season, he barely got any powerplay time, and as soon as he got the extra minutes with more skilled line mates and top PP time, his totals went up, but his production rates were quite similar.
The reality with Marchand is the Bruins did well by finally figuring out what they had, but signing him before it was obvious that he was an absolute superstar. Both Bergeron and Marchand's contracts were amazing value, but I think that's something that became more obvious after the fact than something that was common knowledge at the time of signing, so I don't know there was as much more money out there for them to get than was often said. The Bruins didn't do well on those deals because the players took incredibly selfless discounts, I think they just understood those players worth more than many other teams would have, and those deals ended up being terrific bets.