I don't know what they debunked, but I do know that if I follow my natural sleeping rhythm, the wake-up time keeps advancing by an hour a day. If I wake up an hour earlier to compensate for this, it's really hard and unpleasant to do and I feel like shit afterwards.

So what I converged to is sleeping 2 hours less on weekdays and then sleep in on the weekends. This is marginally better, but still Fridays aren't very nice.

I'm like you. If left alone -no schedule at all- I will go to bed about one hour later everyday.

This is exactly me and I've struggled with it since I was a child.