Alas, “generic Democrats” don’t exist. All the ones we can actually vote for have pesky details, like names and histories. Generic candidates pretty much always outperform specific named candidates. That’s true of Biden, sure, but it’s also true of alternatives to Biden.
Instead, name a specific Democrat that you think will do better, and we can compare their performance to Biden. Who specifically do you propose?
Who is the Bernie of 2024 in your analogy?