Let me just say that this episode was needed for the sole purpose of showing off what else Pokémon Connoisseur's can do. Therefore it's not filler.
To be more precise- It's not a filler in between two canon events; Finding out Opelucid Gym is closed in the start, going to Virbank City in the end.
I mean we were going to find more about them eventually. That's for anyone who thought this episode wasn't needed as Cilan got no development.
To those who do this; Ash has other rivals, stop only talking and comparing any new rival with that one Best Wishes rival.
Unless you lot secretly really like this character, way more than me and thus are obsessed with talking about them... him.