>>12459692evolution does NOT select for the best it only selects against those who are too bad to survive. The tail isn't bad enough to die out so it stays, at the expense of like 90% of males getting killed during mating season from predators. But that doesn't matter because the species survives.
Objectively speaking, the tail is trash. It's energy inefficient and grants no ability and makes the bird clunky and slow, and the peacock would be better at surviving without it. They would have greater numbers greater individual survival rates be faster and more energy efficient. The tail does not give anything, but it isn't bad enough to eliminate the species so it stays.