You're making a distinction about 'privileged' system calls, why, exactly? You really think something like Oracle won't require access to a ton of syscalls to work correctly?
> If you can actually exploit a system call, neither a MAC based approach or a pledge will help.
MAC will, pledge won't.
For example with SELinux:https://www.kernel.org/doc/Documentation/prctl/seccomp_filte...
Linux has added a direct pledge+unveil clone to improve the situation: https://raw.githubusercontent.com/torvalds/linux/master/Docu...
That's not a 'weaker version of pledge', it's part of a much larger framework with much greater enforcement capabilities.
seccomp-bpf is a more fragile version of pledge; you need to keep changing your sandbox whenever you upgrade glibc, because there's no mechanism to keep syscall usage in sync between the kernel and userspace.
It was fine for my case, because I was implemeting my own direct system calls, and froze any external dependencies, but it's typically very fragile across system and dependency upgrades.