Kylo's easily forgiven (because Vader plays favorites) because he doesn't know the cost of the birth of the Empire was. Doesn't know how much and how dearly his family had paid, and paid, and paid, decades before he was born.

"The Force doesn't work that way. It doesn't care how you feel. And atrophied abilities are still there, ignoring them doesn't make them vanish." Ask him how he knew.

Regardless, he'd have to have a talk about things with the tiny Princess.