I'll say it again: the more aft the bike allows you to put your weight going downhill, the more in control you will be going downhill, and the faster you will go.

That's a gross generalization but I'm sticking to it. Just think about your bike/body/center-of-mass as the bike is angled downward.

And downhill geometry has its problems when going up hill.

Skill (practice) is important but basic physics is undeniable.