> C has to make a syscall to the kernel which ultimately results in a BIOS interrupt to implement printf,

That's not the case since the late 1990s. Other than during early boot, nobody calls into the BIOS to output text, and even then "BIOS interrupt" is not something normally used anymore (EFI uses direct function calls through a function table instead of going through software interrupts).

What really happens in the kernel nowadays is direct memory access and direct manipulation of I/O ports and memory mapped registers. That is, all modern operating systems directly manipulate the hardware for text and graphics output, instead of going through the BIOS.

Thanks for the information (I mean that genuinely, not sarcastically — I do really find it interesting). But it doesn’t really impact my point.