Sorry, this is going to sound crueler than I intend, but as for Mahomes, welcome to the NFL. Players get hurt. If you're a fan of '80's Giants, you understand this (Simms/Hostetler). If you're a Patriots fan, you understand this (Brady missing a season). If you're a Colts fan, you understand this (Manning, Luck). If you're a Saints fan, you understand this (Brees). If you're an Eagles fan, you understand this (Wentz). If you're a Redskins fan, you understand this (Theismann). If you're a Browns fan, you understand this (Kozar).
I don't disagree with King at all (I'm not a Reid fan, so...), but as a general proposition, "things happen" in an athletic contest, where you're using your BODY to advance the game.