You can say that about anything. Communism is great, in theory, but its actualization sucks. Having nobility make all your decisions is great in theory, but not in practice. Benevolent dictatorships are great in theory, but there's no clean way to dislodge them when they start to lose their benevolence. Theocracies, tribal elders, meritocracies...

I mean, what is the difference between a council of nobility and a council of land-holding Athenian citizens, where citizenship is an inherited trait? Is there all that much of a difference if 10% of the population gets a say instead of 2%? Not to mention that if you only get a say when you've inherited your title and also own land, then that really starts to sound like a noble class anyway.

Handwaving away "yeah, but slaves, women, poor people was just a thing of the period" just isn't good enough. I'm reminded of Stephen Fry's roar in his Catholicism debate, when one speaker defended past misdeeds by the Catholic church as 'well, no-one at the time knew any better', to which Fry responded 'Well, what then are you for?'. It's all very well to have a feelgood core of a theory, but you have to have the execution of it as well. Lots more has been added to democracy since the early days; it wasn't some sort of golden period of the common person.