Sheer force Couple this with flare blitz and you'll be hitting everything that even resist fire moves with atleast 2 hits. This move as well as STAB has 180 power. Fire punch definitely is not half arsed considering 140 attack + sheer force + STAB. If anything flare blitz is over kill and fire punch is what you can rely on.
Burgh Last time I checked leavanny is 4x weak against fire moves. Heck if you hit it with a lit match it would crumple, so even if you didn't want to grind Hustle boosted fire fang would do. You can catch one in route 4 at level 17, a few levels lower than what your party Pokemon will be. After a couple trainers it'll be level 22, it'll learn fire punch which is the strongest fire move you can get this early.
Level 35 is not a ridiculous time for it to evolve, Drilbur gets earthquake at level 33 and then you can evolve it so its hardly much of an effort. Flare blitz is a couple levels after and this paired rock slide/headbutt is the only moves you need both boosted by sheer force. I think its unfair to say rock slide's accuracy makes it unreliable as its only 90% hardly crippling 70%.
I think it deserves TOP because its the only Fire pokemon to really pack any sort of a punch and definitely out-tiers any Pokemon in HIGH because of how hard it can hit. It comes early in the game and is a pokemon that will be hitting hard all the way to the end of the E4. Despite not being overly useful in the gyms it will still be hitting trainers/team plasma like a truck.