IIRC the average adult female fish lays about 100,000 eggs over the course of their life, of whuch only 2 reach adulthood themselves. The rest get eaten, starve or succumb to disease. It’s about the same for octopuses. So your 1% or 1-in-a-million could actually be 99+%, depending on what you count as sentient.
Even in humans, the mortality rate before adulthood is considerably higher than 1%. So your numbers need updating.
P.S. approximately 100% of antelopes get either eaten, burnt or starved. Not one dies of old age. The same is true of almost all wild species.