Quoting: HabsRafiki
The trade is about as good as the Jets can expect. But why do it?
My assessment of Beck is very similar to yours, and there's already Dach emerging, which begs the question why the Habs would want to blow the bank on PLD, especially if it doesn't include moving Dvorak out. And what about Monahan?
I'll try and answer your questions 1 by 1
Why do it?
I think you can assume with PLD that you are getting a 60 point player acquisition who "plays the game the right way". This is far from nothing.
There is also some small chance that Dubois has another gear and becomes another Zibanejad. Either way he makes this team better.
Finally in the top 6 you ideally want 3 or even 4 centers as we've seen in Tampa, there will be injuries and you need the center depth.
Beck vs Dubois
I know people dream about Beck becoming the next Bergeron, but to me it seems more likely he's just a good player who plays in a middle 6 role. Even if he hits his upside, he'll become a less good version of what Dubois is today.
Dach vs Dubois
You need both of the players AND Suzuki in your top 6 to win. Some days Dach plays wing. Some days Dubois plays wing. Suzuki may even play wing some nights. Giving MSL options and depth in case of injuries is what this is all about.
Where does Monahan fit in?
Monahan is a short term play, Dubois is a long term play. Let's assume Monahan is healthy all year (big assumption) and puts up his best season in 6-7 years (50-60 pts). I would not be supportive of the Habs signing him to a long term deal at 6M+. I think that would be the wrong move for the Habs both because of the injury risk and because he will be declining when this team is getting good.