Dzingel got 2 x 1.8m in the summer of 2017.... he had just turned 25 and had posted 14g and 32pts in his first full season.
Johnsson posted 20g and 43pts and he will turn 25 about a third of the way thru next season... the cap will be about 8-10mil higher next season than it was when Dzingel signed, and Johnsson had a better first season. Based on cap inflation, Dzingel would have gotten around 2.0 mil if he was signing this season.
All that said, I think 2 yrs at somewhere between 2.25-2.5mil makes sense for Johnsson. I believe that would take him to UFA so maybe the Leafs do something a bit longer. I think something longer term below 3.5m could make sense, Johnsson is a good player.