I don't think that's what's happening and I don't think you understand what's going on. He probably feels incompetent because someone he cares about, his sister, got hurt while protecting him and everyone else. He probably felt like he was lacking the ability to protect what he holds dear to him while the one who he holds dear protects him at their own expense. He cares about her he wants to be enough. He is ashamed.
I think he's stopped going out of his way to get their stepdad's attention. I think the growing relationship between him and the FL has calmed his inferiority complex quite a lot.
He more wanted to ensure he could and going forward can protect his sister.
OMG I KNOW HE WANTS TO BE SEEN BY HIS STEP DAD BUT MY GOD SOMEONE SLAP HIS DAD TO GET GIVE HIM ATTENTION. i hope he doesn’t turn evil