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I'm not engineer but:

Cyclist weight on a bike: 60% on the rear, rest on the front.

IMHO, according to your mechanical rules, it's more important to have 2 bolts on your seatpost collar than on the stem.

Weight distribution isn't that relevant. The question is how the rider imposed loadings translate into stresses on the components. The steerer clamp is only about 40mm long, and exposed to large twisting loads. The seatpost clamp has smaller twisting loads and the fulcrum point is typically 75-100mm away from the clamp bolt, where the bottom of the post sits inside the seat tube.