Here's something that GF didn't fully think through. The movepools of Pokemon who get the Rock Head Ability:
Geodude family, Onix family, Cubone family, and Bagon & Shelgon only get Double-Edge.
Rhyhorn family, Aerodactyl, Bonsly, and Blue Basculin get Double-Edge & lesser Double-Edge Take Down.
Sudowoodo, Aron family, and Relicanth are the only ones who I would say probably get the best use of it learning Double-Edge (and Take Down) and Wood Hammer (Sudowoodo)/Head Smash (Aron family and Relicanth). Also Tyrantrum only gets Head Smash, but hey it can make use of that at least.
And no Rock Head Pokemon learns Brave Bird, Flare Blitz, Submission, and Wild Charge (also Head Charge, Light of Ruin, and Volt Tackle but those are Signature Moves and I don't see Bouffalant, AZ's Floette, and Pikachu family getting Rock Head).
Think about it, Rock Head Aerodactly with Head Smash, Brave Bird, Flare Blitz, and Roost new meta. Probably would give its Mega Evolution a run for its money.