10x definitely has nothing to do with salary in either direction - you can't conflate productivity with salary and expect to make sense of the world we operate in.
or there could be another possibility: You think you have 10x engineer on your team, but actually you don't have them. You just keep employing a lot of 0.1x engineers that are unfit for their position/level/grade
I think the latter view is why companies like amazon/netflix fire a lot of engineers that they think are 0.1x or less than 1x