Yeah no one is saying gerrymandering isn't a thing, but to do Picasso , a party still has to control the whole state level process.
When the Democrats lose the Governership, state house, and state senate, in a former swing state like Ohio - it's due to the party, and its message. Especially when it occurs in so many states. It is unfortunate that Democrats don't want to be an inclusive party, and it isn't going to serve anyone.
A handful more statehouse trifectas, and, even if, implausibly, the Democrats retook the presidency and both houses of congress, the GOP could still call a convention, and with 38 states in accordance, change the Constitution directly - entirely bypassing the will of voters in CA, NY, and other Democrat strongholds.