The Vex we see are just construction workers.....like technicians, engineers, and such. Their weapons aren't even weapons to them....they're just transmitters, relays, and hammers being used improperly. Crota struggled with the combat units and nearly died....until Oryx came and saved his ass. Oryx did beat them...but it took him a while. The Vex could send their combat units at us....but so far they've needed us quite a few times. "Why kill something when it could benefit you?" type of deal. They need us to deal with Taken and Hive leadership.....such as Savathun and Xivu. Quria still has a will of it's own...so it might still be sided with The Collective. Then eventually.... destroy The Darkness....somehow.