Washington is the maximum Republicans could theoretically get.
That is a statement of profound ignorance. For instance, Slade Gordon's proposal was five Republican, four Democratic, and one swing seat.
Okay, and the best Democrats could possibly do (think MD or IL) is 8 Democratic, one swing seat, and one Republican. A fair map produced by negotiation between the two parties should fall roughly in the middle of the partisan extremes. We ended up with 5D-4R-1S, which is an awful lot closer to 4D-5R-1S than 8D-1R-1S. Therefore, Republicans got a better deal here, just like Democrats got a better deal in AZ.