The passage of time is a funny thing. It happens in two ways, first slowly, and then all at once.
"Teams of the past" refers to a lot of teams. Would any NHL team today beat the 1940 Rangers? Sure. Would any NHL team today beat the 1994 Rangers? Not so fast, my friend.
Jaromir Jagr goes back to the Penguins Cups in the early 90's, and he is still putting up numbers today at age 43. It is not like the "bigger and faster" guys of the NHL today have made him obsolete. I think the Gretzkys and Messiers and Yzermans and Orrs would not have any problems playing and excelling in todays game.
The game itself has changed, the rules, the goalie equipment, the philosophies of coaching and strategy, etc. But if you evened out these things accounting for the difference in eras, I think you have to go back pretty far to see 2016 teams completely dominating.