The Linux kernel defines syscalls as its stable ABI (note: there are also non-kernel ABIs on Linux, such as Wayland) while Windows defines the DLL calls as its stable ABI.

One isn't better than the other. Linux's approach allows binaries to be fully statically linked, which is a more predictable environment for binaries, but Windows's approach composes better, as every process loads DLLs and this allows for things like graphics drivers and COM to work more reliably. As things stand on Linux you can't use the GPU in a portable statically linked app, because the kernel doesn't define the semantics of dynamic linking.

FYI, Windows's approach is better in some respects, like letting you avoid syscall overhead in some cases.