This is the key sentence from your piece:
Biden took his biggest hit from independents.
Most voters in this country vote pretty much the same way every time - Always straight Democrat or straight Republican. It's those independents, moderates, and undecides that end up tipping elections one way or the other, and, as such, are the prize voters that politicians covet.
Losing independents is a big deal for Biden, just as it would be for any President.
That said, this is not an election year, and things can change one way or the other in a hurry. It is not, however, a good omen, despite all the happy spin the usual suspects will try to put on it.