The distinction is important: someone else already wrote that the -10× person will move you further away from the goalpost, while the 10⁻¹× counterpart is still moving towards it, only slower.

That's a good point. If your team has an 0.1x engineer, you'll still get to your goal eventually. If you have a -1x engineer, you might be going in the wrong direction to ever finish your project.

> a 10x engineer might not exist

10x engineers do exist, but they're vanishingly rare. I actually met one once. He eventually burnt out and left the industry permanently.