Kylington's mistakes are overblown, all high scoring D make mistakes. Brent Burns led the league in giveaways the year he had 70+ pts. Makar, Hughes, Fox make a ton of mistakes every game.
Kylington was unlucky to have coughed up the leafs goal yesterday - he clearly wanted to lift it much higher - it wasn't an IQ mistake just an execution mistake which happens especially when you don't have special teams time to really stay sharp.
What Kylington needs to do to be a #1 isn't on him, it's on the coaches to utilize him as a #1 (so far they're using him like a #4 which is not smart)
Now if he wants the Norris trophy, he will need at least a year or two of experience in a #1 role to get even better, and the game will "open up" and "slow down" to a point where his execution will be flawless. Just needs a chance.