They probably level off a bit, but I said this before the season started, I expected a team that while maybe ends up with roughly the same win % as the last couple years, but doesn't have the wild swings that the last two Bruins teams had. To me they projected out to be a better defensive team in 2016-17 but regress a bit offensively coming off career years from 63, 37, Eriksson, and a red-hot PP early in the previous season.
Go back and look at their records and you'll see multiple runs of 7 or 8 wins out of 10, combined with multiple runs where they lost 7 or 8 out of 10.
I expect this team to be more consistent over the course of 82 games. They are back to being a strong defensive team, players are buying in, system tweaks, personnel, etc. Strong defense leads to better consistency. And they have a decent record despite very little in the way of secondary scoring from either lines 2 and 3, or from the D. It's not all just Rask bailing them out game after game, this team is doing a good job limiting high % scoring chances thus far.
But I don't think Sweeney has a team where he can rest on his laurels and just see what happens. He has the luxury of making a move if it's the right move, but even though I think an 2 and 8 run is less likely, Sweeney shouldn't wait until it potentially happens to start making calls to bring in some help. Fellow GMs smell desperation, which usually leads to mistakes being made by the desperate GM.