Well, that's what vanguardism gets you. It's why e.g. anarchists are fundamentally opposed to vanguardism. The problem with vanguard parties is that once the vanguard party is in power it's now in its own interest to continue being in power and any step towards communism would be counter to that interest. Unless you happen to luck into having a benevolent dictator who somehow against all odds actually is a true believer in communism, isn't corrupted by having absolute power, doesn't fall victim to the bureaucracy and systems of power he commands (e.g. Sankara) and lives long enough to both get into power and use that power to deconstruct the entire system that enabled him, you just end up with a new political class replacing the owning class without also abolishing the working class.

If people didn't fall for people "selling an aspirational fantasy", we wouldn't have made it out of feudalism. Early anti-capitalists just severely underestimated how resilient capitalism is (i.e. most of them did not anticipate Disney selling you anti-capitalist messages as a product, or "late-stage capitalist recuperation"). Given how long Europe was stuck in feudalism it's not at all unreasonable to expect capitalism to be replaced by something better -- as long as you don't expect it to happen in your lifetime.