The democrats having to overcome a 5pt disadvantage (I haven't checked if this is even accurate) would just be because of the lag in the system with people movi

The democrats having to overcome a 5pt disadvantage (I haven't checked if this is even accurate) would just be because of the lag in the system with people moving to blue states from red states. If the reverse happens then it'll be biased in the other direction. It's not a structural bias toward one party or the other. Gerrymandering can absolutely causes biases, but gerrymandering is performed by both sides. Saying it's "consistent" when we're only talking about the past 20 years I think is a bit much.