I don’t think what they thought is irrelevent at all! That is the thinking of the “Living Document” fools. They want to interpret it any way they wish and disregard the context in which it was written. They made sure they included many things and excluded others for a reason.
States having IT is another matter for debate. Federal is different - and IIRC what you state was supposed to be “temporary” (as if that would really happen, but one never knows), as I believe was also proposed/instituted several times over the decades.
The Constitution was amended in 1913-- that's why the Founders' thoughts on this topic are irrelevant. The "living document fools" are the ones who want to change the Constitution without amending it.