I agree with your many of your premises but not with your conclusion. Republicans are consistently primaried from the right and are therefore more responsive to the demands of their base. And, externally, ie. with Democrats in legislation, Republicans are far less likely to compromise than Democrats. (As you mentioned stopping the Garland nomination in its tracks as opposed to the usual process of finding a compromise candidate)

I would argue it's the lack of idealism in Democratic candidates that frustrates voters. Why elect Democrats who don't produce any legislative results they are asking for. Voters overwhelmingly want a public option or medicare 4 all and Biden has stated he would veto it.

I am voting for Biden because he is better than fascism, but that's an incredily low bar. If Democrats want enthusiasm and high turnout, why not give them something to get excited about?