Its hard to say what happened in the 1st game. IIRC, the 1st game against the Rams was on a short week following that gut-wrenching 1st loss against the Lions. Also, I think Stafford had one of his statistically better games of the 2024 season in that first matchup.
I don't want to make excuses for the Vikings or KOC but let's face it - that was also probably the worst regular season game they played right up until the Lions handed them their lunch in the last week of the regular season.
So you couple Stafford playing about as good as he could possibly play at this point in his career with a Vikings team coming off a knock-down, drag-out loss on a short week and you get a flat team performance.
The notion that game was some McVay masterclass is a stretch for me. Is McVay a good coach? Yes. Were the 2024 Rams a good team? Yes. Does McVay enjoy some magical ability to use the Force against KOC whenever the two teams match up? Doubtful.
As for the playoff game, the Lions made it clear what defensive approach would completely neutralize Darnold's ability to function and McVay just duplicated that. That's about as easy as it gets and the reason KOC couldn't answer it was because he couldn't answer it with the personnel he had. The OL couldn't block the pressure schemes and the QB couldn't process the field quickly enough to exploit the gaps the defense left exposed. I wish I could point to an obvious flaw in KOC's approach to that game but there isn't one, and the fact that the Vikings have a completely new interior OL and a new starting QB should confirm sticking with that personnel heading into 2025 would have been like taking a dead dog out that ain't gonna hunt.