“This reduces binary size to just 14kB:”
A {fmt} 11.0.2 test binary starts at 75 kB stripped. Turning off locale support, builtin types and speed tweaks gets it to 23 kB. The last 9 kB drop only comes from ripping out the C++ runtime, swapping exceptions for abort. An empty C program is about 6 kB, so the formatting itself was never the fat. The language runtime was.