I think this is an issue of interpretation.OP does say that mindfulness/exercise/stoicism are helpful and also talks about the sleep-stress deadlock. I think what they are saying is that although these activities help, you need your mind to be in a decent shape to sustain these practices, which can only be achieved through quality sleep. This is to say that even if you have a good meditation practice or an exercise routine, if you don’t focus on getting your sleep back on track, you’ll never be able to handle stress in the long run.