Also - here is a link to a table showing the current carrying capacities of solid vs. several different stranded wire options.
I had to consult with an EE but this took about 5 minutes to "debunk", or at least clarify. Here is the key point that you appear to have missed:
The table below indicates the current ratings of PVC-insulated single and multicore wiring cables.
That derating had nothing to do with stranding. It has to do with individual insulated wires being used in a cable, not single wires. It would apply to two solid insulated wires or two solid stranded wires equally. Basically your whole premise is founded on incorrect interpretation of a chart. Here is a link he sent w.r.t. the electrical code which mimics your chart approximately. He expect those numbers you linked are from an old electrical code.