Yep, the Kanto Frontier Brains were just shown in a brief montage of superimposed images over Kanto. I personally liked the battle, if not only for the fact that Paul just completely flipped out eventually, which is a first for this series. Not to mention he got flattened even worse here than he did when he fought Cynthia. The battle overall lasted at least half of the episode, though.
Reggie's flashback only showed him vs Brandon, and it only showed him with Drapion.