Quarry at least proved his mettle against Foster, Patterson, Lyle, Shavers and Mathis. Even his second tier of victories over guys like Neumann and Spencer are more impressive than almost all of Williams' victories. Quarry is just more proven... and it's not even close.
Quarry never fought a big man who had power COMBINED with the speed of Williams. Williams was an athletic freak, a man who fought on very even terms in multiple fights with men on the same level as quarry(Machen and Terrell).