The USSR was typically very efficient in keeping the authoritarian figurehead in power for long periods of time, not doing anything useful for the average person. The fitness function of attempting to keep an authoritarian leader in power for long periods of time typically fails as it's inefficient, but that doesn't mean such systems cannot last for long periods of time in the right environment.

The USSR failed because it's only purpose was to enrich and empower the single leader. That's why Lenin sticking around wouldn't have actually improved things, either for the USSR or communism in general. He still believed murdering large swathes of the population for "the good of communism" (read "Whatever I like"). In Russia, turns out large portions of the populace can be stolen from, murdered, oppressed, starved, etc without a danger to the god emperor.

Any system, bureaucracy, TTRPG ruleset, etc that prioritizes a single figure over the whole will inevitably erode the value the whole produces in favor of empowering the single figure. It's a matter of accountability. In a single figure system, the only accountability is to the single figure's personal whims.