In the ancient world, republics and democracies weren't practical at anything but the local level. And lands composed of disunified city states were typically conquered by empires. I suppose you could have some sort of empire or monarchy at the top and then a local democracy. Problem is that, without the ability to put centrally friendly local rulers in place, such systems tended to ferment rebellion. Such empires tended to die and be replaced by the stronger, more centralized ones. The strong rose to the top. The others were pushed aside. That's why, in the circumstances of the ancient world, nearly everyone was ruled by an empire. And that's why, under modern circumstances, democracy is rising to the top. Democracy simply happens to be the strongest system now.
Ogliarchy and republicanism was always idiocy. The ruling class has always tried to justify their position by saying that their wealth and power is justified and good. Aristocracy literally means "rule by the best", in an etymological sense. The lower classes shouldn't concede to this bullshit. Don't swallow the lies.
That's why I think that the Roman Republic wasn't really anything ever worthy of respect anyway, and I think there was no real loss in conceding to the practical reality of empire. It was as indecisive as a democracy and as unfair as an empire. All of the bad, none of the good. It was inevitable that Rome would switch to empire, or be conquered by someone who had.