If they were arguing he was 'evil', sure.
But arguing that he's a teen who can't control his anger surely must be relevant to claims of self defence.
Rosenbaum was reported to be aggressive, but not a threat, by the ex-marine who was trying to watch KR.
KR"s maturity and ability to deal with violent situations I would think would be relevant.
Absolutely.
But that comes across pretty amply from his behaviour on the night in question. The problem is that Rosenbaum really was aggressive and really was a threat. He chased KR and lunged at him. The evidence is not that KR hunted Rosenbaum down in a rage and shot him as he begged for mercy.