Regarding stat distribution, only Pyroar's speed is better than any of Arcanine's stats (Sp.atk doesn't matter as Arcanine's Atk is better than Pyroars S.A). Physical bulk is slightly weaker, but there's quite a difference in Special bulk. Pyroar also has an extra weakness, a pretty common one at that, which it got in exchange for an immunity to a pretty rare type.
Level-up method only matters early on. Sure, early on Pyroar is more useful than Growlithe, but not more than Arcanine. You can also get a Sun Stone as soon as you get Rock Smash, at level 35 or less even. The point about delay to level 45 stands, so Pyroar has a 15 level range it's useful in. Having stronger moves is also nothing Pyroar can brag about. Arcanine has 3 120 BP moves (how is Outrage garbage?), Pyroar's only 100+ BP moves are Overheat, barely stronger than Flare Blitz, and Hyper Beam (which makes you immobile for a turn). With that low defense, buffing isn't advisable, Headbutt is bad in the long run, same for Fire Fang.
Arcanine's movepool is better even without CC, which takes hardly any time to get. Just grap a Mankey/Primeape from Route 1, get it 10-ish levels and you're good to go. With the Unown in Citae, grinding is really easy. How easy something is to get doesn't affect how useful it is in the long run, which is the point of this.
Again, no one's denying that it's useful early on. Just that Arcanine is better in the long run.