I have an opinion:
Good NHL lines require footspeed.
Speed down the middle, and speed down at least one wing.
You can have the other winger be slow if they're going to be the trailer, but that's the extent of it.
As for size? Yes, you need some, because you need a winger who can win a board battle and hit the centre or opposite winger with an outlet pass.
So let's look at our effective top line:
Tkachuk - Lindholm - Dube
Why does this work?
You have Tkachuk who can win a board battle and hit Lindholm or Dube with the breakout pass.
You have Dube who can push play forward
You have Lindholm who can keep up with the play, even though he typically doesn't drive play.
Now let's look at our arguable best line in last year's playoffs
Lucic - Bennett - Dube
You have Lucic who can win a board battle and hit Bennett or Dube with the breakout pass. Though he is prone to strange gaffes.
You have Dube who can push play forward
You have Bennett who can keep up with and drive the play.
That's why this line worked.
Now let's look at the other three lines Geoff Ward somehow thought would work tonight:
Gaudreau - Monahan - Leivo
You have Monahan who can win a board battle and hit Gaudreau with the breakout pass. However, this does not happen, because as a centre, he is not positionally supposed to be engaging in too many battles along the boards. He's utterly wasted.
You have Gaudreau who can push play forward
You have Leivo who... is neither a centre nor speedy. And didn't even look coordinated today.
Mangiapane - Backlund - Ryan
You have Ryan who cannot win a board battle and cannot hit Backlund or Mangiapane with the breakout pass.
You have Mangiapane who can push play forward
You have Backlund who can keep up with and drive the play.
Nordstrom - Bennett - Lucic
You have Lucic who can win a board battle and hit Bennett or Dube with the breakout pass. Though he is prone to strange gaffes.
You have Nordstrom who cannot push play forward, and generally was the worst player among the 24 skaters who were on the ice today.
You have Bennett who can keep up with and drive the play.
It just baffles me that our coach thought any of these three lines were a good idea.