If you can do anything to fix your sleep now, immediately, it should be done. Poor sleep is arguably the worst possible thing you can inflict on your body. It has direct links to virtually every major disease and ill health outcome, including cancer, alzheimer's disease, every major mental health disorder, heart disease, increased risk of physical injuries, decreased metabolism... The list continues.

You should absolutely get your diet under control and build a consistent exercise routine in the long run. But both of those things will be very hard to do without the proper dose of high quality sleep every night. Without proper sleep you'll be fighting your own body every step of the way. Every positive health outcome gets harder to achieve without sleep, not easier.

No, and I find it somewhat baffling that so many people seem to think along these lines.

For most people, making major, permanent lifestyle changes is much harder than using a CPAP machine. For people with chronically disrupted sleep, that gap is even wider.

Healthy diet and exercise are free in principle, but you have to choose extremely cheap options for them to actually be cheaper than a CPAP machine in practice.

It's not really "better for" someone with OSA because lifestyle changes alone only have a small effect on OSA severity. It's like going on a low-sodium diet when you have hypertension: it's not a bad idea, and it's almost always good for a few points of improvement, but only an utterly incompetent doctor would recommend it as the sole treatment.

It's a lot harder to control one's diet and exercise when one chronically feels like shit due to poor sleep.

They're both critical. If you only have one, the other will be less effective (lean muscle loss versus fat gain when sleep deprived, a diet that disrupts sleep, sleep onset latency when there's no exercise) and/or more risky (increased injury risk when sleep deprived).

Although, I wonder _if_ the false dichotomy were entertained, what will contribute to quantity and quality of life more.

Completely anecdotal, but I've been both highly fit and obese and irrespective of my fitness leve, crap sleep always makes me feel like junk, and good sleep always makes me feel great. I get more crap sleep being obese, but if I could fix that, exercise is much easier to come by.