Evolution sucks at long term though—that’s essentially your 4: they would be outselected before they would be frequent enough.
However, the “hermaphroditism is only found widely where, for one reason or another, finding a partner and finding them to be wrong sex can be really fatal” (sessile plants, slow snails) suggests it must be very costly indeed, and I’d bet on “simple” metabolic explanation: these adapted organs directly compete in terms of their influence on the body.
Evolution sucks at long term though—that’s essentially your 4: they would be outselected before they would be frequent enough.
However, the “hermaphroditism is only found widely where, for one reason or another, finding a partner and finding them to be wrong sex can be really fatal” (sessile plants, slow snails) suggests it must be very costly indeed, and I’d bet on “simple” metabolic explanation: these adapted organs directly compete in terms of their influence on the body.