Eh. I suppose they had plenty of spotlight, but that doesn't mean it was all good spotlight. Kael'thas certainly had tons more potential, and much more personality than Vashj did. All Vashj had was being Illidan's loyal servant, so as he was our enemy, so was she.
But Kael'thas actually had a big group of a playable race on Azeroth loyal to him. He was a racial leader. And Blizzard squandered him so raiders could kill more notable players for their epic purples because they were whining that Majordomo of the Lich King, Lord of the Firelands, Prince and Princess of the Black Dragonflight now essentially its leaders as Deathwing was out of commission, and a freaking Old God weren't notable enough.
And it's my headcanon that they were trying to build a new Well of Eternity with the water. Think about it. Vashj was gathering tons of water, and Kael'thas was gathering tons of mana. They each had a vial from the Well of Eternity. Together, they could make an extremely powerful source of arcane magic, one that would serve the Illidari well in their fight against the Legion. I believe Illidan had a third vial from the Well of Eternity (unless that was used to make that big pool of souls thing in Black Temple that Kanrethad Ebonlocke talked about in the green fire chain).
So together, the new Well of Eternity would be stronger than the one beneath Nordrassil. Both would be made with three vials of water, but the one in Outland would have the added bonus of all that mana Kael'thas harvested from the Nether.