They might have followed this guide: https://forums.galaxy-of-heroes.starwars.ea.com/discussion/86076/the-perfect-guide-for-the-perfect-start#latest
Did you do the same (this perfect start guide was created after I started)? In any event, there is a limit to how fast they can promote vader and siddious doesn't have much health so he can be easily killed. If you had AA, you could dispell all those negative effects from Vaders crusher and siddious' AoE move.
I could probably help you if you posted a link to your profile