without a big genetic assay isn't it virtually impossible to know whether or not the trait (hydrophobia) persisted due to the symptom itself rather than just a correlated advantageous mutation that brought along hydrophobia as a happy coincidence?
if we need to continue the flawed math analogy; evolution has always done pretty imprecise cocktail-napkin math, even if it has been wildly successful at it.
(Or more precisely, it’s already doing the math, and the current answer is that hydrophobia is the better solution [for rabies’ purposes])