Sounds to me like a clever move.
Thats like saying that Bronzebeard was a bad leader because dwarves build fortresses. Being able to resurrect the dead as forsaken is one of the perks of their race.
And how on earth is expanding your territory a sign of a bad leader, even if he has large reinforcements ? You try to spin it too much here.
Still she helped in the effort and in the end stood above Arthas dead body. Don´t seem so bad to me considering her biggest drive in (un)life was the death of Arthas.
And if anything is plot-armor, it´s that stupid Bolvar-Lavaman thing. That was all kinds of stupid.
Still she was the only one on Azeroth being able to forge that pact and secure the Val´Kyrs servitude. In the end she made the forsaken much more powerful since the Val´Kyrs are the reason for her "limitless reinforcements" in the first place.
I don´t see that much luck to be honest. She made the best of the situations presented to her. She made no mistakes, she led her armies to success and she secured a future for the forsaken. All in all she´s more successful than any other leader in wow.
And if you want to talk about plot armor, why not talk about Lo´gosh Wrynn...