The protagonist is now dark, anti-human, and bad. I don't want to make any excuses. He is in such a state now, so I will describe it according to his state. He will be as bad as he is, and will never leave any room. This is also the process of the protagonist's V forming a long curve. He will also doubt, struggle and explore the truth, but now he is deeply trapped in Dark Side, so his behavior should be like this.
The character's personality and behavior will not remain static, which is also the characteristic of the characters in my works. Of course, I would not write a book with three levels of collapse. The protagonist will naturally return to the light, but this process is destined to be painful and struggling. Light and darkness jump repeatedly? At least I would not create a character so superficially, especially the protagonist.
Don't compare the protagonist's affairs with Darth Koret or Revan, because you are using one part to compare others' overall situation. I don't want to judge whether Tang Xiao is stronger or weaker than Revan or Koret after he reaches the end. All I can tell you is that at least he will be complete.