This is what separates the greats of the game from the rest (something Purdy has every opportunity in the book to do for himself by the end of his career). You just can't give them any time at all with which to work. A great quarterback will take the ball with 2 minutes left on the clock, and 90 yards to go in order to get into the end zone, and will still get you 6 points (PAT pending). Mahomes, time and time again, has shown that he can do just that. Brock will get there (if he's not quite there yet) eventually.
This was a well-played game on the defensive end of things (by both teams). Both offenses left a lot to be desired at the end of the day. But, ultimately, I do think the better team won.
Also, if this kind of a game, and win, doesn't tell you anything else, it should at least tell you that, at the end of the day, experience matters. Mahomes was/is experienced in the Super Bowl. This was Brock's first rodeo. It won't be his last, though.