Well, not the trailer per se, but something it implies about The Empire Strikes Back (that most holy of holies).
In Rogue One, we see X-wings attacking AT-ATs, and being pretty effective at causing damage. This is consistent with other places in the EU as well (Rogue Squadron smokes some AT-ATs in the X-wing novels).
So OK, if X-wing lasers are more effective against AT-ATs than Snowspeeder blasters, then why the heck did the Rebellion send their pilots against them in Snowspeeders? It's not like they didn't have the X-wings ... since the Snowspeeder pilots had to go to a rendevous point to switch ships.
Are the Rebels tactical idiots, did they forget lessons from earlier battles, or am I missing something?