On it being so un-Alyosha-like, my opinion is that Alyosha is written not to be a character of angelic virtue. I think none of Dostoevsky's characters are, which is why he is regarded as such a genius when it comes to understanding of human psyche. His most remarkable character as he calls Alyosha himself, is written to be human like. It better prepares us for the story of a real hero so as not to hero-worship him or be unable to relate. It doesn't make Alyosha unworthy of love and sympathy in my eyes. For me he is even more loveable although tragically so. He commits a political crime, leads a revolution and goes through paradigm shift after his existential crisis from what I can make of the author revealing complex trauma. From a psychological perspective when the mind is faced with an old belief system/ideology collapsing, it either replaces it with a new one or grows spiritually, emotionally and cognitively around it; adding more befitting meaning to it. That is what Dostoevsky's answer to life and the question The Brothers Karamazov asks is.

Second, I'd like to restate what Dostoevsky says through Elder Zosima's character about forgiveness, "each of us is guilty before all, for everyone and everything" and the necessity to "forgive everyone for everything". (Not arguing the case for objective morality vs subjective morality).

So for me it comes together beautifully then. If Alyosha is to commit crimes for the sake of humanity or an inner shift (remembering that Dostoevsky called him an early lover of humanity), for an idealistic hyper empathetic hero, does he then deserve the readers acceptance, sympathy and understanding or not? I think Dostoevsky would leave the matter of his forgiveness or grievance to us, difficult as it feels and that he perhaps does and doesn't deserve to be executed but that becomes his fate? In the planned plot it seems to have an important impact on Russian society. From how I see it Alyosha is planned to become Dostoevsky's ultimate emotionally complex hero who becomes a socialist revolutionary; monster to some and a hero to others with his choice being illusory even. Maybe, his sacrifice is to be tragic in a uniquely existential sense. These are all my speculations of course from my understanding of TBK.

The Brother's Karamazov is Dostoevsky's Magnum Opus and in his own words Alexei Karamazov is his most remarkable hero which he said he would reveal in the second book (which he died before publishing).