As others have noted, one can get deeper and stronger bass by increasing excursion and this might compensate for the smaller cone area vis-a-vis another driver with a larger cone. But in audio, as is the case with almost anything else, there are tradeoffs involved. My favorite drivers are low excursion drivers meaning that I don't go for extremely deep bass. My speakers utilize twin 12" drivers in a Jensen-Onken cabinet and they can go as deep as 35 hz. While this does seem a bit modest, this low excursion driver is very fast and clean and blends well with the horn/compression midrange driver of my system.
A local builder uses 18" drivers, sometimes in twin driver arrays and he says it is good to 30 hz or so. He will soon be building with 31.5" woofers that are rated to 28 hz; I've heard the prototype and it sounds great. It is not just the amount or depth of bass that matters; large driver/speakers deliver a sense of weight, large scale and authority (with no feeling of strain) that smaller systems cannot match. My own system, which is two feet wide by three feet all and about 18" deep is on the tiny side for a horn system and does not have the weight and scale of the systems with larger woofers and much larger horns.