Please note that the Federal elections clause (which you quote correctly) applies to elections to the House of Representatives, and (as amended) to the Senate.
It is proper to refer to these elections as “federal elections”
But notice that Article I §4 does not make reference to the appointment of Electors at all. This is a power reserved EXCLUSIVELY to State Legislatures.
But it creates some paradoxes. For one, it elevates the legislatures to be superior to the state constitutions which created them and gave them all their authority in the first place.
What if the state constitution says all laws, including election laws, must be passed by the legislature and signed by the governor?
Is SCOTUS going to jump in and overrule the state’s constitution?
What if the constitution says presidential electors are to be chosen by popular vote and the legislature decides to choose them based on the vote of the state house?
I don’t see how they can give the legislatures the power to ignore their own constitutions, and I can’t imagine a single state would have ratified the US Constitution if they thought that would be the case.
I guess we’ll see.