The Beach Boys made some really high end virtuoso intricate compositions, and I like a lot of their songs, but their high falsetto harmonies always seemed to be a niche sound to me, not mainstream rock, even in the 60s and early 70s when hard rock hadn't really been developed yet. Also, their California beach scene subject matter always seemed like a niche as well.
Real rock bands were able to have a broader range of rock music style, and also sing about a broad range of topics. The Beatles had this broader thing going for them, but they were a little bit of a niche as well. They had that twangy "Beatles" sound that was still slightly off the mainstream.
I think bands like the Rolling Stones, the Who, Pink Floyd, the Moody Blues, etc. had the sound that really evolved into the rock music of the 70s and beyond. Actually, Paul McCartney adapted to this mainstream sound a lot more after the Beatles broke up, but the other three seemed to continue making weird music in comparison.