libc is used by the entire system. It's not a vendored dependency of just sudo. At best, you'd amortize it over everything that uses it to get a reasonable comparison.
Are we not on the trail to doing the same with rust, at least in theory? You don't think someone somewhere has the idea to make an all-rust system eventually? Even without that evetual ultimate expression, if you have even a few rust components in your system and not just sudo alone, then the same point stands. You don't count rust itself any more than you count gcc.