For one example, I don't think it's a given that the green line (velocity vs % type-checked) should have a negative slope. Maybe in some cases, for some projects or some people, but certainly not universally. At least part of it would have been positive on almost all projects that I've worked on, and I'm not doing rocket science.

Then, the combined chart just looks at the amount of bug-free output, completely ignoring the amount of bug-ridden output. That latter part doesn't just get discarded, it needs fixing, and bugs that were only discovered in production are expensive to discover, debug and fix.

This is in addition to pretty much every other top level comment in this thread, a lot of which bring up important points that are unaccounted for even conceptually in the charts.