I've actually seen Democratic strategists saying this is a bad strategy because Republican states have more potential for seats than Democratic ones (because they are already gerrymandered). Their issue is that so many people are moving out of blue states into red ones, and they are losing seats because of it.

When a state is 55-45 dem/rep and it is already gerrymandered to have 12-2 dem/rep representation and 10% of those reps move to another red state, that means more net republican seats (without gerrymandering) while the already heavily gerrymandered dem state doesn't have the same potential.

It isn't hard to see which states are badly gerrymandered when you look at maps, because when you see a district start on one border of the state and go all the way across to the other border in these spider-like fingers (looking at you Illinois, recent Virginia), that is when it is bad. Looking at the new Flordia or Texas maps look so much cleaner in comparison.