Thanks for your insight, and offering the case history of Smiley v Hom.
However, in the opening sentence of that document, it says the decision is with regard to Article I, section 4 of the US Constitution, which is specifies “the time, place and manner of holding elections for Representatives in Congress” not the Presidency.
The issue under discussion here is with regard to the election of the President, which was originally defined in the separate Article II of the Constitution, Section 1, clause 3, which has been subsequently been replaced by the 12th Amendment.
So the case you cited isn’t a perfect, apples to apples comparison, perhaps.
Not perfect, but it pretty clearly establishes that when the US Constitution says a state legislature "may determine" something, whether it's the process for choosing representatives or electors, they really mean "the state" may determine that thing.
It's almost impossible to imagine any state agreeing to ratify the US Constitution with a provision allowing a majority of the state legislature to unilaterally override that state's constitution.