Absolutely it was. I can have some issues with people's general way of characterizing what Biden did, but I feel like you are still missing the point that I am making:
It is the normal course of political leaders to become corrupted and start to do things like the DNC is currently doing. It happens in Communist systems, it happens to the Republicans, it happens to the Democrats, it happened to Labour in the UK, it happens to any political body just because of the nature of power and corruption, and the incentives at work. This whole idea "Well we have to get rid of the Democrats because they're bad, that'll solve it" is 1,000% missing that point (and, yes, if there were anyone who were saying "We have to keep voting for Democrats, that'll solve it," then I would equally tell them that they are living in a dream world.)
My point is that getting ourselves out of the current crisis involves being engaged with the political system (both in and out of the "official" allowed channels), and that giving up one of the key tools of influence and letting the forces of evil gobble up a giant advantage for themselves in November 2024, which we will now have to work incredibly hard just to get back to even the pretty-bad state things were in before, was a massive mistake. Whether or not Biden was "good enough," or for that matter whether even his significant sins like genocide in Gaza needed to apply to Kamala Harris, has absolutely no bearing on that point.
Again: People have been trying this strategy you're promoting since 1968. It definitely hasn't pulled the Democrats to the left. My feeling is, work to strengthen unions and civil institutions outside of Washington, support progressive candidates (the few of them that exist within the Democratic party), and try to avoid obvious disasters. That makes sense to me. The strategy that it sounds like you're talking about, withholding support until the Democrats get better on their own all of a sudden, has in my view proved itself to be an unmitigated disaster in the years from 1968 until now.