On Linux seccomp is what provides syscall restrictions, and seccomp was originally added to Linux to support untrusted app sandboxing--CPUShare and later Chrome Native Client (NaCl). See https://lwn.net/Articles/332974/. This is why classic seccomp, as opposed to BPF seccomp, only permitted a small, fixed set of syscalls--read, write, and _exit.

A seccomp classic sandboxed process will be at least as secure as any WASM runtime, no matter the engine. Even though the former is running untrusted native code, the attack surface is much more narrow and transparent.