Section 1. The powers of the government shall be divided into three distinct
departments: legislative, executive, and judicial.
Section 2. No person or persons belonging to one of these departments shall
exercise any of the powers properly belonging to either of the others, except...
Perfect example. The commerce clause has nothing to do with the interstate highway system. Article 1 Section 8 gives Congress the authority to build post roads. The idea that the authority to manage elections somehow gives the authority to delegate responsibility to the executive is just wishful...
Article 7, Sec 4 does no such thing, and the rest of your argument hinges on that. You seem to be a practicing attorney. If so, I'm not surprised you read into something that simply isn't there. It's your nature.
"Section 4. The election of officers, and the filling of all vacancies not other-
wise directed or provided by this Constitution, shall be made in such manner
as the Legislature shall direct."
Nice try, but no.
And I'll ask you to think a bit. Where does the TN Constitution authorize the legislature to delegate its authority? Please cite the actual Constitution, not some court case that derived it out of thin air.