If you are so confident, try setting up an alarm to wake yo up 15-30 times every hour of every night, for a year. See what happens to your overall health and to your weight in particular.
And that is moderate sleep apnea. Actually, apnea is worse because you wouldn't even be breathing normally while you are "asleep".
Nobody is overweight from one reason alone. But do you dispute the idea that it contributes?
Sleep deficit drives metabolic changes that may result in obesity (e.g over feeding behavior).