I don't think syscall-vs-C-function is at all meaningful for someone making a completely unrelated language. The system has to pick some ABI for communicating w

I don't think syscall-vs-C-function is at all meaningful for someone making a completely unrelated language. The system has to pick some ABI for communicating with the kernel, and syscalls don't change that. The ISA generally doesn't define how arguments are passed, it's really just in the business of providing a fancy jump instruction. Arguably, using the same ABI for userspace C functions and for communicating with the kernel reduces the amount of work required of completely new languages, because they are likely to need C interop support anyway.