There is a very easy test to verify the “myth” of power over weight vs power. Pick a flat road. Pick a TT bike to avoid drafting effects. Perform 3 runs:
- Weight set at 100kg, power set (via erg mode) to 300W, let the speed stabilize, record the speed at which you settle;
- Repeat, but with your weight set at 50kg;
- Repeat, with your weight at 50kg, and the power set at 150W.
If W/kg drives speed on the flats, as @MRBaldi_T-ZHR maintains, runs 1 and 3 will yield the same result, and run 2 will be much faster. If pure power drives speed on the flats, as the “myth” maintains, runs 1 and 2 will yield similar results, and run 3 will be much slower.
I do believe these tests have been done repeatedly, but nothing like performing an experiment by yourself to prove your point.