First off, I'd like to address the perception that the Habs somehow had a need in those areas. In my opinion, twitter user @felixpotvin put it best. Loosely paraphrased, he tweeted on July 1 that "if your biggest need is your 4th line, congratulations, you just won the Stanley Cup". The Habs didn't finish 15th in the East last year because they didn't have enough players willing to drop the gloves. Almost every piece I've read on the subject has indicated that fighting in no way impacts the momentum of the game. The Habs finished 15th last year because they misused their personnel, and simply did not have enough guys capable of driving play effectively. It's commonly said that you win with guys like Prust (or Moen, or any other tough "hard-working player"). It's all well and good to have "grit" guys like them, but hockey is still about scoring more goals than the opposition. You don't win with guys like Prust; you win with high-skill players producing at an extremely high level. The Boston Bruins didn't win the Stanley Cup because they had a lot of tough players on their team. They won because they had a lot of people who are very good at playing hockey.
The real issue is that players like Prust should represent the cheaper, interchangeable parts of your roster. You can get Brandon Prust's production from plenty of players without committing 4 years and 10 million dollars on July 1. This isn't to knock Brandon Prust; from what I can see the guy played some tough minutes last year and didn't get killed. Brandon Prust, however, is going to be available in some shape or form all summer for about 1 million less in salary and far less term. Brandon Prust, Colby Armstrong and Francis Bouillon are all useful players. They are not, however, players you should ever feel the need to chase on July 1 and overpay.
Outside of clichés and platitudes, I don't even see what the point of having a "tough" 3rd line is. The commonly used explanations are that "it's good to have some (sandpaper/jam) in the lineup", or "you need to be able to grit out a few goals and get to the dirty areas". It's all well and good to say these things, but there's no evidence that these expressions mean anything. I would have much rather seen a 3rd line that could be dangerous offensively (for example, Bourque-Eller-Leblanc) and force the other team to spread their defensive responsibilities a little thin.This isn't me knocking Bergevin for not going and signing some amazing top 6 forward on July 1. I understand free agency isn't that simple, and that when the time comes Bergevin will likely address that need. I'm also not saying I won't cheer for these guys; odds are I'll be just as excited as everyone else whenever Prust does anything. My issue is that these signings weren't ones that needed to be done right away. The Habs have plenty of players who can fill the roles that Prust and Bouillon are going to be asked to fill. Everyone understands that you incur a premium when you sign someone on July 1. I don't see any evidence that these guys are worth paying that premium for.