DeVoe forces Joe to put his gun to his head, presumable through the use of either mind control or telekinesis, but there has been nothing to suggest that he ever acquired either of those abilities.
When Barry reaches the picnic area, we see DeVoe's Mini. The number plate shown should be on the back of the car. In the United Kingdom, the front plate is black lettering on a white background, while black lettering on an amber background is only found on the rear of vehicles.
When the enlightening happens, a police car loses all power and rolls to a stop but, there is still an exhaust plume showing.
Team Flash decides not to call on their friends to assist against Devoe as he has become too powerful to defeat. However, either Supergirl or the crew of the Waverider could have knocked out Devoe's satellites, which at the very least could have bought them some time.