Right, sorry, was thinking of Mega Aggron's attack. Durr.
Anyway, the point of saying Rock Polish was to illustrate that Rock head + STAB Head Smash + Speed Boosting move isn't exactly something new -- in fact, Aggron is faster after a Rock Polish than Tyrantrum is after a Dragon Dance. I fail to see why Tyrantrum would be better in this role, especially when Aggron easily has the better bulk of the two, and while it has two 4X weaknesses - which Tyrantrum isn't going to be living any time soon regardless - it has a lot of useful resistances such as Fairy and Dragon. In addition, Tyrantrum actually loses power because it gives up Strong Jaw which gave it pseudo-STAB on coverage moves such as Fire Fang and Crunch. While the Aggron comparison might not seem obvious at first, it's very obvious how similar they are and the fact that vanilla Aggron is completely rejected for viability should have given you some insight into why Rock Head Tyrantrum doesn't deserve the hype it's getting..
I'd make the Counter argument Tyrantrum benefits more from Rock Head because of Head Smash's obscene power: Head Smash hits hard enough that it essentially eliminates the need for significant coverage.
With STAB, Head Smash reaches 225 power. Unless the target is resisting that and weak to the Fang move (97.5 Strong Jaw neutral fang vs 112.5 resisted Head Smash), there's no reason not to click Head Smash. The main resistors Tyrantrum would have to hit would be Steels that aren't hit SE by Earthquake (essentially, things tanking Edgequake), which includes Ferrothorn (4x Weak to Fire Fang anyway), Excadrill, Chesnaught and Breloom (though he wasn't beating the former anyway, and the latter still hates Head Smash)
0 Atk Chesnaught Drain Punch vs. 4 HP / 0 Def Tyrantrum: 150-176 (49 - 57.5%) -- 93.8% chance to 2HKO
+1 252 Atk Life Orb Tyrantrum Fire Fang vs. 252 HP / 252+ Def Chesnaught: 166-198 (43.6 - 52.1%) -- guaranteed 3HKO after Leftovers recovery
252 Atk Technician Breloom Mach Punch vs. 4 HP / 0 Def Tyrantrum: 170-204 (55.5 - 66.6%) -- guaranteed 2HKO
+1 252 Atk Life Orb Tyrantrum Head Smash vs. 0 HP / 4 Def Breloom: 270-320 (103.4 - 122.6%) -- guaranteed OHKO
Losing power on coverage moves isn't as big a deal when spamming Head Smash and the occasional Earthquake almost completely mitigates the need for coverage in the first place. At most, he'll use Fire Fang or Ice Fang for 4x targets like Ferro or Garchomp (Neutrality means Boosted Head Smash suffices against Lando-T most of the time).
Tyrantrum obviously isn't faster than Aggron with Rock Polish, but checking the calculator, +1 Jolly w/ Max Speed (397) is still faster than Positive Base 130's, which I'd say is about as fast as he could ask considering it'd be DD instead. The flaw in the Aggron comparison is that using Rock Polish as the boosting move mitigates Speed issues, but doesn't solve the fact that, unboosted Base 110 Attack won't get him that far. If Tyrantrum has any niche, it's going to involve something to boost, be it DD or a Band for Wallbreaking. If we're ranking Mega Tyranitar, I don't see why we can't rank Tyrantrum, who has the exact same speed tier, achieves HIGHER damage output with his main STAB, and doesn't cost your team the Mega slot, meaning he can Wallbreak or punch holes for cleaners/sweepers like Altaria or Metagross, if not just shred Defensive cores with something like Gardevoir.
I won't deny there's probably hints of new toy syndrome, but in the context of OU, I feel Rock Head is a genuine improvement for Tyrantrum over Strong Jaw. If nothing else, a Wallbreaker that can do this
252 Atk Choice Band Tyrantrum Head Smash vs. 252 HP / 252+ Def Mega Slowbro: 163-193 (41.3 - 48.9%) -- 80.1% chance to 2HKO after Stealth Rock
252+ Atk Choice Band Tyrantrum Head Smash vs. 252 HP / 252+ Def Mega Slowbro: 180-213 (45.6 - 54%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Choice Band Tyrantrum Head Smash vs. 252 HP / 252+ Def Mega Slowbro: 180-213 (45.6 - 54%) -- 46.9% chance to 2HKO
252 Atk Choice Band Tyrantrum Head Smash vs. 252 HP / 252+ Def Mega Sableye: 216-255 (71 - 83.8%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Choice Band Tyrantrum Head Smash vs. 252 HP / 252+ Def Mega Sableye: 237-279 (77.9 - 91.7%) -- 31.3% chance to OHKO after Stealth Rock
Is something Stall can't leave unaccounted for, whether or not it prepares specifically for it. And with Stall (from what I've heard) being arguably the most common playstyle higher up the ladder, those numbers at least are looking pretty terrifying.