Seems like Sullivan wouldn't put Kessel on the 3rd line because he wants that line to to be more a defensive line. Similar to '17 playoffs, not '16.
So he can deploy top 6 as primarily offensive and bottom 6 as primarialy defensive lines.
Ultimately, you would want Geno and Phil on their own lines, as Kessel is at his best when he shoots in motion and Geno works the best with the shooters who can one time the puck.
Watching last nights game, reminded me how well Geno would work with players who can get open and unload the shot, he would find them and feed them the puck. He set up Rust perfectly in the slot in the first period, Rust had all the time and space to shoot, but he passed the puck back. There was several instances like this with the 2nd line yesterday.
The player not necessary have to be an elite shooter like Neal, just players who can get open and fire the puck, like it was with Kunitz, Blake Comeau, and Talbot(?).