A team with Marchand, Pasta, and Taylor Hall in your forward lines and McAvoy as your #1 is not competitive enough to build around? It's not like all the Bruins core players are aging out here. You bring a center like Hertl, a top 4 LD, and what giant holes are left that require a 3-4 year rebuild?
Bergeron is still playing very good hockey, but he's due for a comedown. Just due to age. And I'm not one who buys into the whole "but his game relies mostly on smarts which isn't as affected with age" adage, because it's the exact same line I was given for Loui Eriksson every time I expressed concern about his advancing age prior to him signing elsewhere. Not that the circumstances of those two players is nearly identical. But assuming a player even of Bergeron's reliability (aside from much earlier in his career) is going to maintain his production from one year to the next is an optimistic view in my mind and you can't count on it.
With that in mind, Brad of course is well on the other side of 30. Taylor Hall is a player I really like but isn't going to "get better" at this point. He's also not at the same level as Brad and Patrice. Add Hertl to the "not likely to continue getting better" pile given his age.
The best spot to be in for SC winning teams are having a balance of top 6 players on the upswing and guys at their peak. Along with obviously other intangibles. I don't see that happening based on this current roster construction.
Now of course there are actual players who I don't think see it my way at all. Example a. Taylor Hall. He signed here because he wanted to be in Boston and he seemed to genuinely feel this team could contend for the foreseeable future. I hope he's right. But I'm not counting on being Cup contenders any time in the very near future and I don't think we have the assets to pull off a quick fix one way or the other.