If you let a WR catch the ball moving laterally across the field around the Bills 45, that's not the worst thing in the world, you just can't allow a quick hitter where the player has momentum upfield where they can gain a chunk in just a few seconds.
What is crazy is that the two people you absolutely can not let get open are exactly the two who caught those key passes, so I understand the criticism.
In fairness to Buffalo, the whole KC offense showed up to play and it wasn't cut and dry that they could just play man defense and take out any single player or two.
Mahomes fired a rocket on that pass to Kelce and hit him perfectly in stride. That arm strength and accuracy is not common, but it's required to stay competitive in a game like that.
Again, the failure was on the kickoff. Basically stupid to have not squibbed it and gifted them the the 25 yard line with no time off the clock.