In my group (all new players) this mission was very hard for Rebels but in hindsight they weren't far from winning it.

I (imperial) learned from my last defeat and basically turtled in the south corridor. I knew I couldn't spread myself thin enough to cover all the terminals.

I knew where the AT-ST arrives and that's why I picked the south one to defend.

I let them have the north one uncontested. The east one they would have had but they took a bit longer than they should have to get through the door, kill the nexu that kept dodging every attack and pass the attribute tests, which allowed me to spawn some more droids behind them. I eventually wounded one which made their tests even slower.

Even after all that, not really rushing, it still came down to the last couple of rolls. They had to kill a nexu and a door in the last turn to make it and they just failed but not by much.

Things to note.... seems like we screwed up because I didn't see that you needed to pass the attribute test twice per terminal. I'll have to read that mission again. We were just doing one success.... even then, a wounded hero will struggle.
Secondly, I still had the "stun a hero near the door" option which would have helped me win regardless.

Thirdly they had Luke Skywalker unlocked at this point (first side mission) so that helps with splitting the group up, and he can attack doors etc...

I think an experienced rebel group can do it especially if they get a powerful/favorable side mission before it.
I feel like the imperials don't get enough threat to redeploy things in the first few missions.