Is A Coordinator owning BOTH a Growlithe and a Vulpix OP?

I'm thinking of writing a story with a coordinator eventually aquiring a Vulpix and a Growlithe. Is that too much? Arcanine and Ninetales have both been referred to as legendary pokemon. I KNOW they are not actually legendary pokemon, gamewise speaking, but everyone always seems to have one or the other. (Version Exclusiveness not withstanding) So what should I do?

I don't see why you can't make it work. 'OP' is relative, and it all depends on what kind of teams you give the character's competitors. Are they up against veterans or newbies? And perhaps by having two fire-types as their best Pokemon, you can make their team suffer from balance issues even though the fire-types are really good. There are lots of things you can do to make the team feel special but not cheap!

Honestly, there are ways for every team to be beaten - OUs to UUs. It all depends on how you write it, be it for battle or for performance. The scenario is only as cheap as you write it, especially once you take into account the relativity of other characters, their teams, and their level of experience.

As the others mentioned, it all depends on the execution. I think as long as you showcase your Pokemon's strengths and weaknesses, you should be fine. With that said, a coordinator having two fire types can make for some interesting performances.