But dragon knights weren't active during voidwoken invasion, so why would they bother to join and later "betray" Lucian later on?
It could very well have been their inaction during the events of D:OS 2 that helped convince them to take a side before Divinity 2. According to the Divinity 2 backstory, they joined rather late in the war and helped turn the tide against the Black Ring forces.
Also, just because dragon knights were not part of the D:OS 2 story doesn't mean they couldn't have been dealing with voidwoken in their own territories.
