So like using seccomp with a whitelist (fairly easy to do) with per-object access rights.

I'd love to see a comparison of landlock to restricted containers.

Comparing landlock to containers isn't really an apples to apples comparison. Containers use a bunch of linux security mechanisms together like chroot seccomp and user namespaces to accomplish their goals. Landlock is just another building block that devs can use.

Fun fact: because landlock is unprivleged, you can even use it inside containers; or to build an unprivileged container runtime :)