Larson is one of those guys where I'm curious to see what a deeper team with a (presumably) better coach does to his overall contribution. Maybe with a Johansson and a better cast of characters on defense and up and down the lineup will be a positive on the score sheet.
I expect there will be a bump in his counting stats simply from better overall talent (regardless of whether it's on his line or not) resulting in a lower percentage of D-zone deployments. And also better coaching to the whole squad. If there is no bump in counting stats, then I'm still not worried, as he is nowhere near the bottom of the talent ladder on this Sabres roster.
All that said, I wish the deal was for 2-3 years, HOWEVER, with the expansion draft coming, I can see the logic in (potentially) letting his contract expire such that there is one less player to contemplate protecting.