This is quite honestly the most laughably bad take on the Bruins situation that I've ever read. I can honestly debate your take line by line:
The defense as it current stands is pretty bad. However, they have Colin Miller and Joe Morrow ready to go this year, and Carlo, O'Gara, and Grzelcyk in Providence who could all possibly make an impact this season. Don't rule out an early season trade, either.
That's just wrong. McAvoy and Zboril, along with Carlo whom you left out, have legit #1 upside at best, but are likely 2s. They also have Lindgren, who along with Lauzon, also have #2 upside. That's 5 defenseman with #2 (or better) potential coming into the system likely in the next 2 years, some of them potentially in Boston by then. That's not even counting if the previously mentioned O'Gara and Grzelcyk work out at all. True, they lack a bonafide bluechip #1D prospect, but a whole ton of #2's might make up for that.
Glad you can see into the future. After being a borderline playoff team while working in young talent (Pastrnak, Spooner, Krug), what makes you think they're going to suddenly fall off a cliff and be way worse? The drop from Eriksson to Backes will not be that big as Backes is a better fit (even amid the supposed decline), and with everyone a year older, along with working in more high-end talent (Vatrano, possibly Heinen), they should arguably be better this year, which would actually mean a playoff berth.
Because frankly Boston is in a situation that none of those other teams are, whether you actually want to admit it or not.
-Chicago has real money problems, and with how they've treated some of their younger guys by their 2nd contracts, why would Vesey go through all this to go somewhere he'll be traded from in 2 years? That's not to mention the fact that Chicago has had to move so many picks/prospects to maintain their run that they don't really have a farm, which is why they need someone like Vesey in the first place.
-Pitt went all out going for the Cup, and are in somewhat of the same situation. They have a weak farm, which not much hope coming along any time soon, and are currently over the cap for next season.
-Toronto and Buffalo are in the same situation -- both have good strong prospect pools, and Toronto even has Babcock, but neither team has shown they're capable of winning anything yet, and neither has an established core (Buffalo is closer to one, but even that's in the air with Kane's issues). Toronto also can't fit Vesey in with all of their bonuses without moving someone.
The fact is, Boston is currently a playoff contending team, with a proven core (who I think you believe are way older than they are), as well as a top 5-10 prospect pool with legit depth at all positions, which is something pretty much no other team can say. They also don't have much in the way of money issues, and have even gone so far as to PLAN AHEAD for someone like Vesey coming in (they left both cap and bonus space available for him). Especially given that he's from Boston, why wouldn't he want to come here?