Unless it's icky and rainy outside, I generally find it difficult to stay asleep much past 7am. Even when I need it from staying up to 2am too many nights in a row.
I rather suspect it's staying up past sunset that's "unnatural", rather than waking around sunrise.
There is a wide variety of circadian rhythms, yours is just one of the most common, but it does not make it any more "natural" than the others. Some of us are night hunters, and no sunset can give us a sufficient kick.
I rather suspect it's staying up past sunset that's "unnatural", rather than waking around sunrise.