for sympathy, sure she can sympathize with her the undead and the blood elves but that's it she even states that she is not capable of relating in many ways besides the undead and blood elves, and sure she does protect the forsaken as a people but have you really thought about why she does that?
she doesn't protect the forsaken because she believes she has some responsibility to them or something, no, she only wants to protect because she doesn't want to die, she sees the forsaken as a "bulwark against death" seeing that if she dies she will go to hell
she protects the forsaken for her own selfish needs, and before that was the case she was so determined to kill the lich king to gain revenge she payed no regard to the amount of forsaken that died in order for her to get revenge and when the lich kig was killed she didn't care that her people would probably die without her or that the horde may be defeated all she cared about was her own selfish needs.
there is even a quote where as sylvanas states very clearly after the lich king down fall that she didn't care about the forsaken or any race for that matter anymore and she didn't care if the horde she only anted to die but that finally happened she went to hell and saw the nightmarish eternity that awaited her and at that time a Valkyrie approached her and rose her from the dead.
Now her only goal is to never die and to be immortal in a sense, everything she has done for the horde or for anyone was an actions to get her that much closer to fulfill her selfish need of living forever in the disguise of a helpful deed to others.
She doesn't care about people she only cares about whether they have some way of making stay alive forever.
and as for leader ship I do not believe that having a person with a plethora of mental issues,extremely violent tenancies,who also surrounds her self with the image of death,hopelessness,pestilence,sadness and darkness.Someone like that isn't someone you follow it's someone that is let off the leash by the leader in order to destroy the enemy.
Someone who plots schemes and murders her way into immortality isn't someone you want to trust.
And I' not saying baine is exactly a good fit but he a certainly better fit than sylvanas