In other words, it's OK not to be paid according how well you do your job, but according to your negotiating skills?

You pay the asking price if the product provides you enough value. Negotiation is simply setting the asking price, which is absurdly mundane in a free market economy. In fact, not setting an asking price - thus letting the buyer decide what he pays - contradicts norms.

The metric of “how well you do your job” is highly subjective anyhow; between an employee, their manager, their product manager, their coworkers and HR there would be significant variance of opinion.

1. Negotiating skill is a skill as any other soft skill.

2. If somebody consider that he doing the same job (have the same skill) it doesn't mean that it's true.

If negotiation is not a skill that affects your job performance it seems unfair that it has such a big influence on your pay.

That’s how sales work unfortunately

Just because something is currently "perfectly normal" doesn't mean it should remain that way. People should be incentivized to do good work, not to be good negotiators (unless their job involves negotiation).