The species has evolved with feathered wings so that ALL peacocks should be capable of flight.
I expect the peacock, as with other species that have transitioned from flying birds to ground based birds, will have some that can fly and some that cannot. Certainly there would have been a time, while evolving from flying birds to flightless birds, when some ground based avian species could fly; and some could not. So I do not know why you insist that ‘ALL’ peacocks, not inflicted by mutation or disease, should be capable of flight.
The point I was making in Darwinian Dead End No 10 was that most of the flightless birds species saw some adaptive reason for growing stronger legs and smaller wings. The peacock however does not appear to have evolved the large tail for any obvious selective advantage. The large tail makes it harder for him to fly, run and hide from predators. The only advantage the large tail appears to have is in attracting a mate. And that in actual fact the large tail would appear to be advertising a liability. Hence it is a Darwinian fallacy.