The problem isn't just minutes, it's shifts.
You need to roll out 4 lines because in the normal flow of games, players need a few minutes to get their aerobic capacity back to normal, same with three pair of defensemen.
When you have breaks, TV timeouts, etc., you can double shift your best players, but you're going to have to play the Lehtera's and Manning's on a regular basis, whether you want to or not.
I'm not sold that Sullivan is brilliant, he looked good in Boston in 2003-4 when he had Thornton and a hot goalie in Rycroft (.926S%).
Two years later, Thornton gets hurt, and even with Bergeron, Leetch and a deeper team, and Tim Thomas replacing a slipping Rycroft, he misses the playoffs with a mere 74 points and gets fired.
When he took over from Johnston, they played a little better, 71 points in 54 games v 33 in 28 games.
But that was an "all veteran team" - Sullivan didn't play anyone younger than 23 other than Maata on the 3rd D pair.
Crosby (29), Kessel (28), Malkin (29), Hornqvist (29), Kunitz (36), Cullen (39), Bonino (27), Hagelin (27), Fehr (30)
Sheary (23) and Rust (23) were inserted in the second half and the playoffs - Sheary and Rust both spend 1+ seasons in the AHL after college.
Same on defense: Letang (28), Daly (32), Dumoulin (24), Lovejoy (31), Maata (21), Cole (26), Schultz (25)
Dumoulin spent 2 years in the AHL after college
And what carried them to the Cup was a hot Murray replacing Fleury.
The only big changes last year was promoting
Guentzel (22), after 3 yrs in college and a half season in the AHL.
Wilson (24), after college and 2 AHL seasons
Having Fleury and Murray combine for a .929S% in the playoffs will make any HC look smart.
Point is Sullivan has been coaching a deep, veteran team, where young players were well "marinated" in college and the AHL before they were promoted, with great goaltending. So he hasn't had to "coach up" young players.
This season they added Sheahan (26), Oleksiak (25), Simon (23), [Czech with 2 AHL seasons), Aston-Reese (23) - good depth moves
At the TDL: Brassard & 2018 3rd for 2018 1st, 2019 3rd and Cole
Still the same team, led by a group of veterans, with "marinated" young players gradually incorporated into the mix.