A lot of the comment section highlights the obvious problem: this is fine theoretically (maybe even obviously correct), but much harder to get right in practice.
On top of that, it’s only even maybe-obviously-theoretically-correct if the employee stays a long time. If they stay for 5-10 years, I’d think rapid improvement tends to beat current ability. If they only stay for 1-3 years, though, the quick learner likely provides less value. Even if they catch up after say 2-3 years, they were providing less value while catching up.