You cannot gerrymander a state - so the Governors and Senate seats are discounted.
Gerrymandering and creating safe districts is an outcome of having already won elections - its not what caused Republicans to win elections. State Legislatures redraw the boundaries after every census - and to draw more R districts, you have to already have taken control of the State Legislature (i.e. won an election).
Not to mention you have to deal with the Voting Rights Act in many states. Here is an example we dealt with in Texas during that process. There was a "swing" district represented by a Republican. It was "Majority minority", but was represented by a Republican. When lines were redrawn the last time the Democrats highlighted that district and got it redrawn to ensure that a Democrat would win. It wasn't about being "majority minority" and creating an opportunity, it was about ensuring a Democrat won the seat. Sure enough, the D won the seat in 2012.
Hilariously, the Democrat they elected did such a bad job, the District elected a Republican in 2014 - despite it being (numerically anyway) about a 55-45 D district.