Considering Old Major's dream for the future and his warnings to the animals, how is the ending of Animal Farm ironic?

Old Major's dream envisioned an earth of the future with
no humans, where animals ruled the world and determined their own actions. He pointed
out that all of the evil in the world was the result of humanity, and declared that the
animals should all maintain an "enmity" toward humans. The animals should avoid all
human characteristics, even after they have been conquered. By the end of the novel, at
least one part of Old Major's dream had come true: The leaders of Animal Farm were
considered equals among their new human associates, but the pigs had broken nearly every
commandment in the process, from wearing clothes to walking upright. The other animals
were now worse off than they had been under their human masters, working longer hours
for less sustenance. The animals were all equal, but some were just more equal than
others.