Well, that was interesting.
In Canada as well, municipalities also have no legal rights. Councilors and mayors are allowed only by the whim of their respective provincial government. These people can be replaced at any time for any reason.
Your legal reasoning did not fully make sense to me. Either I need to study it more fully and perhaps some re-writing is warranted.
And as I understand the Constitution, the states can adopt a system of PR as well--with no legal interference from Washington or the other states.
The 17th Amendment took 30 years to effect. It might be quicker to build the TDG.