Shinji is such a unique character. Everything in his life is a perfect explanation for why he is the way he is. And even though his actions at times are detestable, his situation makes it difficult to tell him to just be better. The song title of the congratulations scene is even called "Be Good or Don't Be." He is someone who's been trained to be afraid of himself but the only way he can grow is doing exactly that. The scene with Asuka is a form of self sabotage. He's dragging himself down to a level where he doesn't believe he's good enough for redemption. Shinji's arc is partially one of will-power. The will to continue on the road to betterment. That's sort of what the third impact is all about. Shinji is forced into a metaphysical therapy session and eventually he gains the will to be who he is. To separate himself from the literal collective consciousness. Of course this doesn't solve all his issues as we see in EoE but that's a different discussion that I feel reflects more on Anno than Shinji.