Kerfoot had limited PP time (0:36/GP) and had 20 ES points good for 150th in the league. That is top 6 production while being a pretty reliable two-way player.
2021 Playoffs: 7GP 1G 5A 6Pts
McCann was 5th on the Penguins in PP time (1:59/GP) and had 10 of his 32 points on the PP. He also had a pretty unsustainable s% this year.
2021 Playoffs: 6GP 0G 1A 1Pts
I do prefer McCann's potential, especially defensively and as a shakeup to a semi major part of the lineup. However he has had some playoff struggles and is arbitration eligible in a years time so his AAV might end up being worse ultimately.
It isnt as black and white as you are making it seem.
Regardless its a moot point, I bet he's not taken. Like I said, Im expecting a "you scratched my back now Ill scratch yours" agreement between Francis and Dubas. Dubas had to give Hakstol permission to go.