Income equality is outcome equality, which is unenforceable.
I suppose you can do a No True Scotsman and say that those weren’t truly enforcing equality of outcome since there were people at the top of that society doing the enforcing, but most would find that argument pretty strained.
Everyone should have the chance at getting educated, but not everyone needs to pass or excel - it is up to the individual to succeed, but it is up to society to provide the opportunity to succeed. That is why schooling (primary, secondary and tertiary) should be free for everyone.