If there's anything that Arcanine SW can actually tech into, it'd be Magmortar.
The question is... Does Magmortar need it? I mean, look at Fire Blast. 20 for each energy on Magmortar? So an activated Scramble, and 2 fire energy attached does 100 damage? For no backlash? On a pokemon we're already charging as an attacker? Do we REALLY need Arcanine? I... Don't think so. Maybe as a back up hitter, when Magmortar's about to die. Even then, you should be using Typholosions to power up a second Magmortar on the bench when that looks like it might happpen soon.
Extra power looks nice, but redundancy doesn't, especially if it just barely damages the active better then Magmortar. If it did 10 more damage to OHKO Blissey, Garde LV.X, and Gallade, then I'd be all for it, but since it doesn't...