If the GOP didn't gerrymander and suppress everything in their favor, I would agree. The path to 2018 will be incredibly important if Trump hasn't been impeached before then, namely by preventing further voter suppression from occurring and striking it down in various states.
The numbers I've read before or that with the current state of gerrymandering and other suppression efforts, Dems need about +7 to take the House. So they have a harsh disadvantage, but there's nothing the GOP can do in a situation where they're 16 points down to save themselves. If we get a D+16 election you start nearing the point where the GOP gerrymander backfires, and districts they built to be safe +10, +15 places are falling.