Actually, I came up with the correct model. It's two swinging arcs that meet in the middle at 0-degrees. I'm gonna just skip the whole buckt and rope experiment because it doesn't really represent the forces on a spoke; there's no fulcrum on a wheel to leverage the spoke. I'll come up with a diagram that shows why the forces on a spoke are always in tension and then I'll build a test-jig to measure spoke-tension increase and hub-windup as a function of torque on the hub. Then test two identical wheels with different lacings.

Actually your last diagram will work for testing. We can keep the bucket and torque tangential by wrapping the rope around the hub-flange. Actually I'll use a chain-whip and hang a weight off it. The hub cannot be attached to supportive bracket, but rather should be built up into a wheel. Then clamp the bottom of the rim into a vice. This gives the strongest-torque scenario, such as in the case where our Olympic champion is sprinting with all his might while his bike is held stationary aimed into a wall.

I'll have two gauges, a tensiometer on the spoke and a dial-indicator on the chain-whip to measure hub-windup.