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Yeah this is exactly right, if you can trust the contributors to not code-golf or otherwise Goodhart the LoC metric, then it's a reasonable measure of complexity.

It doesn't work as well when you start mixing languages, or generating code.

Less LOC also doesn't imply simplicity: just look at the demoscene, which often has the former but not the latter.

Demo scene or other competitions that aim at using little space / shortest way to achieve something are not really a good counter example.

TFA includes a time measurement though, and 5 years for 18'935 SLOC doesn't scream quite "how simple something is".