To me the biggest mistake JB made in his tenure as the Canucks GM are the 2 following moves:
1). Louie Eriksson signing.
2). Overvalue of Erik Gudbranson
I don't think JB envisioned Eriksson to declined this significantly after his 30-goals season in Boston. He probably expected atleast 20 goals and 50 points productions in the first few seasons of this contract and clearly it hasn't been the case. Right now Louie is taking up $6 million in cap space and clearly these money could be better spent else where to address either scoring at the top 6 level or offense from the back end.
I think JB overvalued Gudbranson right from the beginning. At the time we acquired him, Gudbranson was 24, RHD who plays physical/throw-back style of hockey. JB was trying to address both physicality and depth on the blueline by acquiring Gudbranson. He saw Gudbranson as someone who can be an anchored of the Canucks blueline going forward. He saw Gudbranson eventually develops into atleast a #3 D-man. Unfortunately, Gudbranson is better off as a #5/#6 D man. At the time JB didn't see the trend of the modern NHL D-man are trending towards speed and skill, and Gudbranson's play style just doesn't fit the current era of hockey. Gudbranson would of been great during the dead-puck era, and he just isn't suited for this new era of hockey nor can he be the go to guy on the blue line. He is better off as a depth and supporting D-man.
If anything, it has shown that JB has learned his lesson. Since Eriksson, JB has stop throwing around money/term on the big fishes at the UFA market, he just brings in depth guys in short to mid-range terms.
He realized his mistake with Gudbranson and in the 2018 draft, he shows that he understands the trends current NHL style D-man and drafted Quinn Hughes.