Like anything some is good too much is bad, a gradient work for a complex society, a brutal difference like kings and dark ages poor eventually bring collapse

Wealth inequality was not the defining aspect of the relationship between kings and peasants. It was also not the reason for the collapse.

The defining quality was the mechanisms by which kings extracted wealth from peasants (indirectly, through layers) which doesn’t resemble what we have in western liberal democracies today. Things like tallage and arbitrary taxation, labor dues, mill/oven/wine press monopolies, heriot, merchet.

Serfs were legally bound to the land.

The Black Death killed 1/3 of Europe’s people, giving peasants leverage because without enough workers, lords could not enforce arbitrary dues because peasant could walk out or revolt, such as the English Peasants’ Revolt of 1381.

That’s when the Dark Ages extraction model started to break down. Not because of wealth inequality, though it can see why they get conflated.

If we take the top billionaires in western liberal democracies today, they do not extract wealth from the average worker (there’s no duress, for instance), and it is clear that they have created more wealth than they have “taken”.