"If you look at the GitHub contributions that I've made, I've made 2967 of about 3000 commits to the compiler source over that time frame. In that time I've added roughly 4,062,847 lines of code to the code base, and deleted roughly 3,753,677 line of code. [..] It means that for every one of those 750 lines, I've had to examine, rework, and reject around 5400 lines of code."
Yet a 750 loc codebase sounds like someone with very little experience and a few days or a long weekend.
I'm not saying only the trivial "some languages are denser than others", but also that it would be interesting to compare projects in total lines of code written including all commit history, and that it would be interesting to compare people's experiences and project designs in terms of "how many times something got implemented in several ways before settling on a final version", or "writing once and the design got set in concrete because it was too big to bother changing", how many prototypes that work differently were explored before deciding - and what that does to people's skills, and to project designs.
I'm guessing thousands of lines of F# would make you more skilled than the same thousands of lines of C#, even moreso if the F# was higher-abstraction than the C#, would you agree?
For the purpose of evaluating experience you count the total amount of code written, not the final codebase size. Four million lines of code is a fair bit of experience in any language, even if most of those lines were later deleted or replaced.
It's low if you're comparing languages based on the skills of experienced programmers, but most programmers are not terribly experienced. A comparison of languages by programmers that are novices to the language is still meaningful. A language that is easier for a novice to pick up and write good code is at the very least one good measure for the quality of the language.