This is not a theoretical debate, we have direct example from USSR. There is no guarantee that a start run system won't have elite capture, but the dynamics are fundamentally different. For example, people like Musk or Bezos simply didn't exist in USSR. You could have status if you were high up in a party, but that just meant having a bigger apartment. Max salary was capped at 9x the minimum, and it was actually scientists and engineers who had the highest salaries. So, the way you advanced within the system and got higher status was by contributing. And we can also see how this quickly changed after a transition to capitalism when an extractive oligarch class appeared overnight. It's a clear example of how systemic incentives directly affect the outcomes.
Also, a single party state actually has a far higher incentive to be seen as legitimate by the public because everybody knows that when things go wrong the party is to blame. The power of the party is directly derived from social stability. Meanwhile, in liberal form of democracy, parties can just play hot potato with responsibility. If they lose an election they then somebody else gets to run things for a while, and then they get back into power like nothing happened.