You brought it up.
Cap space is a huge factor in the 21-22 Avs team. You dont just insert a $12.5M McDavid magically on that Avs team without removing the difference in cap space. Any hockey fan with a mathematical brain not playing in Vegas rules would know and consider that. So yes, insert McDavid's x points on that team, but remove Kadri's and Lehkonen and Helm's contributions and boom, they maybe dont win it then. So +McDavid, -MacKinnon, -Lehkonen, -Kadri, and -Helm.
In terms of contracts, The Avalanche were lucky/fortunate/strategic enough to have Duchene making $6.5M I believe when MacKinnon's RFA contract came up and they locked him up long term for $6.3M and he immediately blew up making that the best deal in hockey. Not that McDavid didnt deserve it, but the Oilers gave him $11M off of his RFA deal and he took them behind the woodshed only signing for 3 years before his next 8 year big payday. You can give McDavid credit for playing amazing right out the gate in the NHL, but then at the same time, argue that the bad Avs teams in a round about way built that Stanley Cup winning team.
Either way, MacKinnon has a Cup and McDavid doesnt.