A lot of team became bigger/stronger and a few teams gained an advantage by going smaller and quicker. That trend will probably continue until a tipping point in 10/15 years when the league is smaller/quicker on average and a bigger checking team starts throwing their weight around and wrecking the smaller teams.
Sports are cyclical.
It wont take 10-15yrs.
If i missed something didnt the Caps just win with Brooks Orpik, Devante Smith-Pelley and Tom Wilson wrecking people. You need balance and obviously enough top end skill to be able to score.
Having enough size and strength to wear teams down will always be a mode of creating an advantage. So can a vastly superior goaltender. So can having a big speed advantage or like Vegas a intensity and work rate second to none.
As far as the OP's question. Gone are the days of a knuckle dragging 4th line and that's been for a long time already. I mean long enough that the Red Wings with Draper Maltby and McCarty were playing effectively. So 90's
Typically it's a top scoring line that gets the bulk of the Offensive zone starts. In a perfect world you also have a line that takes the bulk of the defensive zone starts and then its a couple lines with a decent balance that can find success at 5v5 without being sheltered and have enough versatility to provide secondary scoring as well as responsible defensive play
It really depends on the type of depth the team has and who is best suited for that defensive zone starts role.
Scoring 1 - Scoring 2 - Checking - Energy line .....is how i see it with typically Scoring 1 getting top minutes followed by the checking line and Scoring 2 basically in the same ballpark depending on personell and the Energy line getting the least minutes and responsibility.