UGH this line! the longer i've been obsessed with this show and this character, the more i feel like i understand why this would be so impactful to house.
because what would it mean to him, to hear this from the father who abused him and ground into him - in ways both spoken and unspoken - the idea that house wasn't deserving of love, that he was in constant need of punishment, that something inside him was fundamentally wrong?
"you were right. you did the right thing."
it would be a complete shift from what house grew up with. always feeling like he couldn't do anything right, that he'd be alone forever, that he was a disappointment, that he would never be anything close to the son his father wanted, insert various horrible things that john probably said to him growing up here (or taught him via abusive punishments).
on first glance, getting some version of "I love you" from his dad seems like something that would be meaningful, but for house it would probably either 1) come across as a lie, or 2) (more likely) it would simply fall flat because his dad's love - regardless of the degree to which it may or may not exist - was never enough to keep house safe from him.
but to hear "you did the right thing?"
from the man known for his brutal, unflinching honesty? from the man who told house all his life that there was something wrong with him? from the man who showed house through his actions that "fixing" him would be a neverending battle? from the man who has always been just as obsessed with being right as house is?
it would be real. knowing what we know about house's dad, it would be the most genuine show of respect possible (and isn't respect infamously second best to love?)
and even though it would be a statement about house, it would also say something about house's dad. it would require john to admit, on some implicit level, that he was wrong about his son. and i don't think that's something that has ever happened in either of their lives.
"you were right. you did the right thing."
"you aren't rotten to your core. you are worthy of respect, and you deserve love. i was wrong about you."