It's kind of amazing that the NHL even tried 1-vs-16 for a couple of seasons, particularly in an age when teams had to fly commercial. The Flames in 1981 had to figure out travel to Chicago, Philadelphia and Minnesota in the first three rounds and then it would have been Islanders in round four. It also threw into chaos who you could face in subsequent rounds because it reseeded each time.
With 21 teams, it was easy to do a balanced schedule. 20 opponents, play them four times each. Divisions were meaningless, which was good for the Flames as they were in a division with the Islanders, Flyers, Rangers and Capitals.
Eric Duhatschek had an interesting article on this just year:
https://www.nytimes.com/athletic/536...at-duhatschek/