That's possible, and that's part and parcel of what I was originally talking about. Regardless, it was very inconsistent until Chronicle, and being planet-sized was a description the Titans lacked in early material like the UVG or in-game lore. We also don't know what Sargeras is stabbing in your picture above, it doesn't have to be the surface of a planet, and that also implies the dragons or drakes in the image are themselves the size of planetoids (or large enough to also see the curvature of a planet).