if you wish you were me right now, it's natural
The issue I had with Growlithe was that I had to baby it for so long in order to get the moveset I really wanted. While you are not by any means required to do this in order to use Arcanine viably, it makes it a hell of a lot better for sure. If you want Flamethrower+Crunch, you have to go all the way to level 39 as a Growlithe when your starter (if you chose to keep it) is already fully evolved. Most of your Pokemon will be fully evolved at this point, actually. Hell, even Scraggy evolves at 37, but at least it gets Hi Jump Kick to smack things around with before it evolves, making it a lot easier to use as a Scraggy until it evolves. But if you want Flare Blitz (and Outrage, I suppose, since it comes between Crunch and Flare Blitz), you have to wait until level 45. Admittedly, when I did this, it probably was not my best option even though Arcanine immediately began to show its usefulness as soon as it evolved. I don't know. I could see Numel being placed over Growlithe sheerly because while its availability is much farther along, it is much easier to train and evolve into Camerupt. However, I have only ever used Growlithe in BW2, so I don't want to argue for Numel as much as I want to bring up points against Growlithe.