The solution is, of course, a comprehensive election fairness bill along the lines of what Democrats have already proposed but that Republicans standing on their filibuster left for dead.
Failing that, a nice pro-democracy decision by the Supreme Court in any of these gerrymandering cases that come their way would be nice. Of course, with the Court’s current composition, that’s also never going to happen.
Democrats really do need to start gerrymandering more in order to increase leverage on Republicans on this issue, because no other tools are available. Once Republicans see Democrats are willing to do it too, in equal proportion, in a kind of mutually-assured electoral destruction, their incentives will change, and they’ll get in a more compromising mood.
Tl;dr sometimes you gotta be cruel to be kind, in the right measure