was something the founders didn't forsee,
I disagree because they gave the states control of the election and it was argued in the Federalist Papers. They understood well the ramifications of a "wrong" system.
"Every government ought to contain in itself the means of its own preservation. ... a departure from so fundamental a principle, as a portion of imperfection in the system which may prove the seed of future weakness, and perhaps anarchy. It will not be alleged, that an election law could have been framed and inserted in the Constitution, which would have been always applicable to every probable change in the situation of the country; and it will therefore not be denied, that a discretionary power over elections ought to exist somewhere. It will, I presume, be as readily conceded, that there were only three ways in which this power could have been reasonably modified and disposed: that it must either have been lodged wholly in the national legislature, or wholly in the State legislatures, or primarily in the latter and ultimately in the former. ". - Alexander Hamilton
I think you underestimate the extent to which the Founders understood government and politics even if they didn't have the word 'gerrymandering'. You don't create a democratic system without understanding the potential risks of what happens in an election.
it's a threat to democracy
I disagree. We have a unique history of expanding the rights of the individual. We have trended toward more open and freer government even if there are instances of bad governance. There are ways around gerrymandering through gubernatorial elections to veto district maps (which apparently was the GOP strategy in 90's election to break the ~40 year hold of democrat power in legislatures and their gerrymandered districts, is what started CA to a non-partisan committee). You are closer to your local and state government which you are more apt to change. You have a tough job to justify such threats when the trend has been considerably favorable.