I didn't have as extreme a reaction as this, but I do agree that Edelgard came out of her route looking less sympathetic than when I started it. Still a better option than Rhea, who is certifiable, but not by that much.
I'd rather have Rhea myself. She only goes psycho when she gets betrayed by her...child/mother/grandchild (the relationship between her and Byleth is wack), reminding her of that whole "genocide of her almost her entire race" thing. Edelgard is a lot more calculated in choosing to go to war, allow research into turning people into monsters and allying herself with the actual most evil people in the setting. Rhea when she's sane is not perfect by any means, but she's not going out of her way to start continent spanning wars at least. Plus having played the GD route already I know Edelgard is outright wrong about a lot of things. Her take on Seiros' relationship with humanity is totally skewed by her lack of knowledge of why Seiros actually went to war with Nemesis. ---