Larsson to me seems like a guy that will fall off a cliff in a couple years. This along with the Montour and Stephenson contracts are going to be brutal in a few years.
Therein lies the only potential "downside" with this D.
Right now, Seattle's D should probably be the envy of the league to an extent. Dunn-Larrsson as a top pair, Montour-Oleksiak as a 2nd pair, and Will Borgen alongside either Evans or Mahura on a 3rd pair.
When you need a shutdown, put Borgen and Oleksiak together.
When you need a goal, put Dunn and Montour together.
It's honestly perfectly constructed, and at $27.5m total cost, not offensively priced either.
But, their current roster as is, isn't good enough. In 3 years, this D could be a shadow of its former self.