It's kind of counter-intuitive, but the election of a Democrat in Alabama actually provided a lot of discouraging data about gerrymandering. While a Democrat won the state-wide popular vote, if those votes had been cast in the House districts, Republicans would have won six of the state's seven seats. Gerrymandering doesn't really help as much in a Senate race, but in House races, it's everything.
What is unquestionable is that in a very tangible way, Garland would have provided a crucial vote here. He would have been on the court with a Clinton presidency, instead a partisan extremist is. The path to progress is by participating in the current system so that you hold power to make things better. Things would have gotten better directly on this issue with a Clinton presidency. So if you’re not participating because you think that’s the quicker path to progress, I think this issue provides a large point against that logic.
Howard Dean pursued an explicit "fifty-state strategy" as chairman of the Democratic National Committee in the mid-2000s, putting resources into building a Democratic Party presence even where Democrats had been thought unlikely to win federal positions, in hopes that getting Democrats elected to local and state positions, and increasing awareness of Democrats in previously conceded areas, would result in growing successes in future elections.
The strategy was gradually abandoned after Dean stepped down from the DNC, and I believe that a large part of the Democrats' losses since then is exactly a result of your mindset, since abandoning red states or districts as lost causes only allowed the Republican Party to grow even stronger in areas where it was unchallenged, resulting in lopsided losses for Democrats in even more races and killing any ability to lay the groundwork for future victories.