The "Plans" option should be removed from the menu when the plan used on the Jira instance is not Premium, and this should also include the site-admins point of view.

Currently the site-admins see this:

Those that are not site-admin have this view, which is the most accurate one:

I assumed it was a short term marketing thing, which is really very ill thought out.

— Workaround —

The above suggestion ticket relates to Plans in the top navigation bar.

Under the new sidebar navigation, users who don't want to see Plans can configure which items are visible to remove Plans from their sidebar navigation.