No, landlock is a separate thing. It's the first of its kind on Linux that doesn't completely suck, like seccomp does (https://blog.habets.se/2022/03/seccomp-unsafe-at-any-speed.h...).
The list of syscalls any code anywhere in the system calls is not a published contract with any guarantees.
> You could just
… is doing some heavy lifting here. "You could just" all but guarantee that your program will break in a couple of years for all users who do the responsible thing?
Sure, if you're building an appliance with a support contract, where you control everything, then that's doable. Servers/desktops/laptops, not so much.