So what else could their third spec be?
My suggestion;
A ranged Earth/Magma based spec with a few hints of Void corruption;
Utilizing Deathwing's offensive abilities from HotS that offers two sets of abilities depending on what form you're in;
https://heroesofthestorm.fandom.com/wiki/DeathwingDestroyer provides the most damage and mobility, making Deathwing a flexible brawler. This form is best suited for dueling heroes and chasing.
World Breaker has more range and utility, providing a lot of CC and area denial. This form is best suited for engaging fights, poking, and setting up allies.
What do you think the third spec could/should be?