I wouldn't pay too much attention to the "tiers". Consider it a general list of things that may be helpful, and assume that the relative importance of each is likely to be different for you.
I've never found exercise to be a particularly important part of my mental health, but in lockdown I've become utterly dependent on it. It provides routine, structure, control and a sense of progress - all of which I was getting more of in other places before but which I'm now lacking without the exercise.