Bergevins eras are as follows 2012-17, 2018-2020, 2021. Let's just get the last one out of the way. You gave a great synopsis on this one already so no need to delve. It was horrific. The retool that took place between 2018 summer and 2020 fall was actually pretty decent, MBs one saving grace. It set up a foundation for HuGo to start a rebuild with instead of doing it from scratch like other bottom feeders teams. The first era, I disagree with you @habshalifax. It was awful. He should've been fired after the 2017-18 season. Everyone knew it. But Geoff Molson gave him a second chance so he could begin his retool, which as stated above, was pretty good, but should've never happened under his tenure. When MB got the GM spot, he had a young Price, Subban, Pacioretty, and a 3rd OA pick. Instead of bolstering his team to become a real contender, he went total bargain bin and played it overly conservative under the notion of not sacrificing the future for the present. The most obvious example is the infamous 2017 TDL. Well that's great and all if all his drafts from 2012-2017 didn't absolutely suck.
I'm usually pretty temperate when it comes to MBs tenure but that's only because of his retooling years. What came before and afterwards if isolated, is probably the worst GMing in Habs history with context