Good use of manager time is to figure out what those people do differently and then have them teach their ways to the others. This will, in effect, "improve the whole system" as someone else put it.
Put another way: when there are individual 10x performers on the team (note that this is 10x the average, not 10x the worst), there is also massive untapped training potential, and management has already failed to make use of this. If anyone should have a bad performance review in that situation, it sure isn't the individual contributor who didn't get the tools they needed to do the job! It should be the manager who didn't give them those tools.
That said our business has a tendency to overvalue individual contributions over team contributions. My going example is that a person that spends all day getting other people unblocked on their issues might well be the greatest facilitator of productiveness in the team, but they will appear to be the person that never gets anything done.