Final result IS done by engine upfront (thats why you can't change anything 5 minutes before game start), unless you change something in the game (subs, formations, attitude, focus).
I played one of the most famous managers for years, and then I decided to do some experiments. I saved game just before start, and lost 'cause one of my players got red card (penalty). Then I loaded the game, replaced player who got red card with another player (but changed nothing else), started the game and result was the same. Replacement got red card in the same minute giving away penalty and I lost...
You are taking this game too personally... It's just a game with it's own rules, it's not AUTHENTIC COPY of real life football... For God's sake, in real football you can't pick up some random guy on the street and make him better than Messi, CR, Pele and Maradona together... And someone who is willing to spend few hundred bucks can do it here... Is it fair to other players who can't afford it? Sure not... But, it's this game rule, accept it and play... or walk away... No one is forcing you to play...