We're not discussing a binary, though. Negotiating skills can't completely untether compensation from qualification/performance, but they absolutely loosen the two. If I am a junior employee who is skilled at negotiating comparing my salary with a senior employee who is not, the delta will be far smaller than if our qualifications were the same but our negotiating skills were reversed.
Nah, it's finer grained than that. Negotiating skills are the cherry on top, but they are dependent on performance.
You can't negotiate if you don't have offer a level of performance that justifies the negotiation.
You won't even get the interview (and therefore opportunity to negotiate) without the "performance" i.e. actual work related skills.