If I recall correctly the "point of divergence" is supposed to be some event towards the end of Grave Peril.  So things like Morgan being Harry's mentor won't happen unless he became that mentor  after Grave Peril.  And I don't see that happening.   
 I think "Evil Harry" is Harry without his allies, at least the allies we have seen him with: KoTC, Alphas, Murphy, Waldo etc....  Harry isolated and on the run from the council, making the bad decisions out of desperation. 
 Perhaps something like this.  Harry trades ammorachius and Michael to save Susan.  Susan is freaked out, still human, and wants nothing to do with Harry because PTSD.   Michael is dead / turned.  Charity and the rest of the family want nothing to do with him since Michael never came home from the vampire ball.  The war happens later when the red court is better prepared, council doesn't blame Harry for the war, but he wasn't recruited into the wardens.  Harry learns the wrong lesson and doesn't clue in Murphy and the others , trying even harder to protect them ,so Murphy keeps distrusting him, etc.

Ruthless? absolutely
Sadist?  maybe, but if so it's combined with a strong " pain is an excellent motivator / pain is the best teacher " position.  I don't think she's taking pleasure in inflicting the pain, but in the end result.

The statement that none of us are really free, makes me think of a t-shirt I saw once.
It read " I'd be Unstoppable if not for Law Enforcement & Physics."

Negligent homicide of the sort Rudolph committed? That's Murder in the second degree, and being a cop he SHOULD get an automatic upgrade to Murder 1.  Unsure if Illinois has capital punishment. Doesn't matter: no body, no murder is how the prosecutor will see it.

I'm not sure Mab would appreciate just anyone violating the accords without getting caught, but for her Knight?  While she would absolutely punish him for getting caught,  I think it's fair to say she considers it a training exercise in ingenuity and cunning, so long as he doesn't get caught. 

oh, I'm a pizza snob.  I will eat fast food pizza if it's put in front of me out of politeness to my host, but I'm not going to go there myself.
Frozen pizza?  nope nope nope.
So I totally get where you're coming from Mira.

I put "Wicked Faerie" in quotes because I also disagree with the simplistic view of Mab as "evil".  She's cold, ruthless  and apparently driven by logic and reason to an inhuman degree (though she clearly does have strong emotions). But all that just makes her, well, inhuman.  Which she is. 

Fidelacchius burned Harry.  Because the mantle, supernatural "wicked faerie" power was influencing him. 
Yes his grief and anger were feeding it, but the mantle was, if not running things, then it was definitely guiding the details his actions.