The Job Import Plugin includes an option to "Install required plugins" when importing a job.

When this option is checked and the resulting import is successful, then the "success" display should report details of any plugin that was installed..  or a statement that no plugins were installed.

Without such reporting it is very hard to work out if job import is actually resulting in any plugin installation.  My target Jenkins is managed by Kubernetes and so it is critical to know such details so that they can be included in JCasC...  otherwise these plugin installations will not be permanent.