Here is my case for why rebels may/should dominate for at least when only the core is out.
1. Luke
Has much more mobility over his Father and with it a built in light saber throw because his gun for some reason has pireceing. So he can go around picking off key units pretty well. And unless there is a mobility force cardVader just isn't scary enough for me. Luke can just get to where he needs to be easier.
2. Armor.
The mini walkers have two ways of being brought down, Vader and rockets. Vader should be easy to avoid if the walker doesn't walk toward Vader and with its big blaster it seems like it'll be able to aim and shoot most of the game if you get it on a good vantage point which it can because it has the climbing ability.
The rocket launcher is a weakness but the amount of shooting and having to take a reload action from the looks of it. Just doesn't seem worth damaging a walker. So maybe if there is a fast reload upgrade and the rocket launcher and regular troopers can shoot at different things, then maybe it's worth it but until armor gun platform is going to be hard to bring down.
3 Troopers?
Too early to really say that rebels will outclass their stormtroopers counterparts. But I think they will have more versatility, there shooting has 1/8 more of a chance to hit than a trooper, but also 1/6 more of a chance at dying. Stormtroopers stay alive better by themselves, but almost have to aim to be able to be threatening. Rebels instead of relying on aim can dodge, over and over and over. So in addition to being naturally more punishing, they can also just dodge and be able to stay on an objective much more reliably because the might as well have cover 1 when they take a doge action so focus fire isn't nearly as effective.