I would argue that the Constitution treats members of Congress and presidential electors, and each one’s relationship with state legislatures, very differently.
*Members of Congress are “chosen every second Year by the People of the several States” (Art. I, Sec. 2, par. 1) or “elected by the people thereof, for six years” (17th Amend.) while for presidential electors “Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors” (Art. II, Sec. 1, par. 2).
*While electors are appointed in whatever manner each legislature chooses as cited above, “The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators.” Art. I, Sec. 4, par. 1.
I would argue that the very language of states controlling the “manner of holding elections” for members of Congress is more circumscribed than the language of appointing presidential electors in such manner as each legislature directs. That “such manner” sounds like a “whatever manner” to my ears. 
Moreover, the time-place-and-manner power for congressional elections is shared with Congress while the manner of choosing electors is entirely up to the various state legislatures.
*Lastly, there are age, citizenship, and residency requirements for members of Congress. (Art. I, Sec. 2, par. 2 & Sec. 3, par. 3) but absolutely no requirements for presidential electors beyond that they not be members of Congress or hold federal office (Art. II, Sec. 1, par. 1).
I would argue from these points that the Constitution intends presidential electors to be creatures of the states while members of Congress are not. Even when the legislatures chose Senators, the power to regulate the manner of holding their election was shared between the states and Congress while the manner of appointing presidential electors wasn’t. And the fact that no qualification of age, citizenship, or residency was placed on electors but was placed on Representatives, and more tellingly on Senators even when they were chosen by the legislatures, emphasizes that the state legislatures could choose whoever they wished as presidential electors but not members of Congress.
Let’s boil it down to an example relevant to the proposition that regulating faithless electors is constitutionally the same as a legislature dictating to a member of Congress. If a state legislature made posting a bond a condition of being on the ballot to be a member of Congress, with said bond forfeit at the legislature’s discretion, either that’s not a regulation of the time, place and manner of holding elections or it is but Congress can supersede it because the time-place-and-manner power is shared between the states and Congress. Whereas if a state legislature made posting a bond a condition of being appointed a presidential elector or being on the ballot as an elector, with said bond forfeit at the legislature’s discretion, nothing in the spartan and sweeping language of Art. II, Sec. 1, par. 2 says the legislature can’t.