It's not that wild. Brazeau was undrafted, and Toronto had a decent look but wound up letting him go. So clearly lots of knowledgeable folks were unconvinced along the way. But the Bruins took a punt and it seems to be paying off. Like everyone else here, I like what I'm seeing. But it's still an uphill battle for a guy like Brazeau who lacks foot speed and has only middling hands to make it stick at this level.
What he needs to be is smart. If you look at a big guy like Nick Ritchie, who actually did have natural talent to the point of being a first round selection, he failed in the NHL because, to be blunt, he was too dumb. Brazeau though seems to have some savvy about him and a decent hockey IQ. If he keeps reading the game well, making smart plays and getting in good areas, he'll give himself every chance to cement his spot. I hope he does - the Bruins could definitely use a guy of his size and skill set. But there's a ways to go yet on that road. In the short-term he'll probably have to fight off Maroon for a spot. All he can do is keep making his case.