I think that there should always be more work, but there should not always be more critical work. This minimizes idleness while allowing non-critical tasks to be pushed aside when handling emergencies.

For example, my team has a backlog of work to be done. There are certain things that cannot slip. There are plenty of things that could be pushed out to handle a production outage, or a shiny object, etc.

Indeed, critical dead after critical deadline is a good way to burn out. One a year is critical in a well planning system if that.

This seems like an assertion that may need to be challenged. I'm not convinced a team with no downtime is working at maximum output, let alone maximum efficiency. My experience is that teams that are constantly busy are rarely working on the most important thing, either for the short term or for the long term.

Isn't that poor planning? I never want a team "busy", I want everyone to see where we are going and why.