Was Trump losing a blessing in disguise for the GOP?

[Pessimistic Antineutrino]

No, because the way in which he lost ensured that Trump and the GOP are still one and the same, which is objectively a bad thing. For electoral prospects in the immediate future, probably yes. Biden seems to be a weak incumbent and may very well lose a rematch.

It's a blessing in disguise for Trump, because he lost by a slim enough margin that his claims of fraud are semi-plausible, his base remains intact, and now he gets to be the de facto opposition leader while hand picking candidates that will run as Trump allies in a GOP-favoring midterm environment. All of this sets the stage for a comeback in 2024, or for a Trump ally to run.

If Trump won, 2022 would be Blue Wave part 2 and 2024 would be an open seat race following 8 years of an unpopular Trump administration. Best case for Dems, aside from the whole "8 years of Trump" thing and probably a 7-2 Supreme Court and thus probably no more Roe.

If Trump lost by as much as polls said he would (Biden wins ~350 EV, a few more Senate seats flip) then the national GOP more likely seeks to separate itself and move on, which is objectively better for party and country, but GOP candidates just continue along the populist/culture war track that they're already on, just minus most of the Trump pandering. Or maybe not. Probably depends on the state.