Virgil only wanted power out of the fear of his own safety as well as an alternative to his lack of purpose. Kael’thas is only a spoiled individual who abandoned his own people.
I possess knowledge of this since I do indeed sympathize with those who have no purpose.
One of the worst story developments Blizzard ever went with, all to make him into a loot pinata for Burning Crusade. What made Kael’thas an awesome character in WC3:TFT was his dedication to his people and his willingness to pursue any path to save them.