NPR's morning edition had David Ignatius to basically argue the same point this morning - that Biden is too old to be president.
Ignatius cited polls in which %77 of people (across all parties) think Biden is too old to serve, without engaging with the reality that the Republican/right wing portion of this %77 will probably agree with any negative assessment of Biden. His suggestion is that both Biden and Harris step aside, which would mean that the Democrats would have start a primary process this very instant, literally as I'm writing this. It's the middle of September in the year before the presidential election!
I'm probably echoing some of your points, but it's incredibly frustrating how absurd this whole proposition is. If your main goal is to prevent a Trump presidency (Ignatius believes this, and essentially says as much), the most risky thing you could do is sacrifice the incumbency advantage and run through the primary process.
Most of the party leaders, Democrat and Republican, are very old. Trump is very old. Biden was very old when the party coalesced around him as the candidate in 2020. At this very moment, we see Diane Feinstein and Mitch McConnell - two politicians holding important positions in their respective parties - visibly struggling to perform their duties as a direct result of their age. A narrative that focuses its gaze on Biden, specifically, and suggests the Democrats flip over the chess board for 2024 by demanding he step down is disingenuous and dumb. I'm continually stunned by how bad national political reporting and analysis is.
To end on an up note, stuff like this is why I'm a subscriber.