Needs more context
Kadri was playing third line center the whole year. He was not playing as a wing with Nylander/Tavares and sometimes Matthews and Marner. Kadri had connor brown and Marleau as his linemates for most of the year.
Yes kadri did play top pp unit but he was playing in a greatly reduced role with fewer touches than the previous season. Last year was a down year for kadri. He has been very good on Colorado. He is still comfortably more valuable than kerfoot who does not generate a ton of his own offense like kadri used to do.
Kerfoot being younger may offer some hidden potential which dubas valued highly but Kadri is more than 1 million dollars better than kerfoot as a player right now.
I would not say Kadri has been "very good" on Colorado. His ES/60 numbers are some of the better ones of his career, but not significantly better than in Toronto at any point besides his near PPG campaign in that lockout season. He's also played a bit on MacKinnon's wing this year so he has had the same kind of benefits as Kerfoot has had. His PP numbers are a lot worse there than in Toronto, but I do not know if he's on the top PP with MacKinnon or not. If he is, that is very disappointing.
Kerfoot's PP numbers have dropped a lot since Colorado (since our 2PP does not do a whole lot) and his ES/60 numbers are the same as Kadri's in the same role, minus the fact that Kerfoot has played some wing with those players this year.
All in all, Kadri may be 1 mill better than Kerfoot right now, but it's not much more than 1 mill better based on their respective play this year.