The exceptional demagogue got way better results than Thucydides ever did. Athens was destroyed by Nicias and his friends, not by Alcibiades or Cleon or any of the other blowhards Thucydides got butthurt by. Behind every dead democracy: the Eternal Oligarch.Its golden age is glorified while its end days are regularly compared to the modern west. That seems fair.
You can crap on Thucydides for being a bad historian but he's literally the first one (that wasn't obviously just making shit up) so he should get a pass. His theory is that Athens let a exceptional demagogue lead the country off a cliff - not that extreme of a theory.
EDIT: Also two plagues.