So you want:
A. The Habs to retain.
B. To add Thompson
C. To accept only a 5th Rounder as Sweetener.
D. To believe someone will take on Backes at the Trade Deadline.
What you don't get is:
A. Backes is barely an NHL 4th line RW at present.
B. He still has TWO years to go on his contract so no one will grab him at the TDL.
C. The fact he has TWO years left reduces our Cap flexibility for the 2020-21 season.
D. Why do we do Boston any favours?
Backes is the type of guy that, if you retain half of his contract at the TDL, you might have a team offering a 2nd round pick for him (See Plecanek type trade for reference).
So, the point of this trade for the Habs is:
A) Get out from under a bad contract a year earlier. Backes buyout next year is roughly same AAV, but one fewer year.
B) You make some room for rookies. Habs have 25 NHL contracts so they need to do quantities for quality anyway.
C) Worst case scenario, you get a 5th to take on an extra $2.625M of cap unused cap space this year & save a year of buyout money when money will be tighter due to the young guys.
D) Best case scenario, you flip Alzner, Thompson, and unused cap space for a 5th and say a 2nd rd pick as well.
Yeah, of course, this helps Boston, but this also helps Montreal a fair bit.
Short-term advantage goes to Boston.
Long-term advantage goes to Montreal.