The pummelo is just about the best citrus fruit. But the ones you can buy in a supermarket are not very good.
Truer words were never spoken!
The pummelo (or "pomelo") just doesn't seem to grow well under U. S. soil conditions. My experience of traveling to Asia during the past 40+ years indicates that you gotta go to Vietnam (ask for buoi) or Thailand (order som oh) if you want the real thing. And for me, the native Asian pommelo is definitely the world's tastiest citrus!
A bit of good news from the home front, however, is that U.S.-grown pummelos seem to be getting better. Ten years ago they tasted just like grapefruit. Now you can find them with a taste that's 50% or even 75% like the Asian versions.
My guess is that quality has improved as a few growers in Texas or Florida have found a way to improve the soil chemistry of their orchards. Let's just hope the taste of the American pomelo will someday rise to Southeast Asian levels!