I tend to agree with some things mentionned here. Ultimately, Bergevin being a former defenseman would not have accepted any deal for Subban that would not have involved a skilled capable defenseman coming back (he even said so himself in the press conference following the trade). Otherwise, it would need a good overpay from a team with only a rookie defenseman, along with great forwards to make up for the hole created on defense, prioritized by the GM.
Simply, the Oilers' only chance was to offer a big package for Subban including Nurse or Klefbom + high forward talent + their 1st. And as already mentionned, it was reported the Canadiens' management wanted Pier-Luc Dubois badly. Columbus stealing him with the 3rd was most likely the end of conversation for Chiarelli and Bergevin, assuming Chiarelli wasn't too keen on giving Bergevin what he was asking for, reported to be Draisatl + Nurse + 1st (PLD).
I'd add to that the fact that it was likely very important that the Habs were not adding their 9th overall (Sergachev), in the trade for Subban. It gave them a window to cushion the loss of Subban with their own pick.
As another poster said, I'm pretty sure not many Habs fan would have been happy with the return whichever it had been other. Be it Weber, Nurse+Draisatl+1st, Barrie+Duchene, etc, no Habs fan wouldn't have been angry because we simply didn't want him to be moved at all. It's not the return, it's the fact he was traded in the first place, the fact that the team lied to us by repeating over and over he was not being shopped when he actually was. And I was one of the very adamant one on defending management on that... It certainly feels like a big betrayal from our team.
But I am happy with Weber coming in too. I hope it's for the better of the team, really, as the GM assures.