That's been most people's experience growing 'Brazos Belle'/'Wilma' in Florida. Apparently it does better in its home region of Texas, but here in Florida the humidity seems to make virtually all the fruit drop off prematurely, so they don't do anything like a proper ripening. I have occasionally gotten a few fruits of this variety to stay on the tree long enough to what seems close to a full maturity in September, and the flavor was ok, but not nearly as good as the other Mexican varieties.
It is for this reason that Hopkins Nursery, the wholesale source of most of the Mexican variety avos in Florida, has stopped propagating 'Brazos Belle'.
In the Gainesville/Ocala area, we've had much better results with Mexican avocado varieties 'Opal'/'Lila', 'Del Rio'/'Pryor', and 'May', which is probably the same variety as ''Joey'.