I'm pretty sure negative 10x-ers exist though. The people who can build something but it then takes someone else 10 times longer to iron out all the bugs ad performance issues.
In fact, I think these people are often mistaken for 10x-ers, especially in their own mind.
What makes the (far more common) negative outliers most vexing to deal with is not just that they're +10x-ers in their own minds -- but that they're mistaken for such in the minds of upper managers (and/or their investors) -- for a great, great while, in many cases.
And having to explain to someone that they need to "flip" their +/- 10x bit on one of their "star performers" can be a really, really awkward situation to be in.
In fact, I think these people are often mistaken for 10x-ers, especially in their own mind.