If they succeed then aren't they an acceptable fit for the role? If it devalues the role then that means the job isn't as demanding as the title makes it seem.
Yeah that would be great is success meant "sound engineering that meets the requirements and is delivered on time without generating friction with stakeholders or adding unneeded complexity". Unfortunately on some companies that don't actually ship much of what gets engineered success means "we got to the next financing round" or "our skills got noted by upper management so we are still allowed to hang around". Bad engineers survive in the last two environments and at the same time stockpile credentials about how many years they were senior at Google or Lyft or whatever, but they really can't actually engineer anything most of the time.
The definition of 'success' varies. If you mean 'completed the project on time with decent quality' -> then no, that doesn't happen as often as with tried and true experts.
When I said 'success' I meant: 'achieved a basic level of competency after bungling one or several projects, often with unknown or unquantifiable bugs and then move onto the next company / role with few consequences'.
More succinctly: caused harm to others/ project and still got a paycheck.