I know you won't understand this first part at all, but a global ecological and climate disaster due to our fossil fuel use up is already baked into the system. If we stopped using fossil fuels now, the world would still increase by 2ºC, which will be devastating for the whole planet.

But we aren't stopping. In fact, fossil fuel use continues to increase exponentially. Thanks to Obama, the United States was the largest exporter of oil in the world at the end of his term: https://archive.thinkprogress.org/obamas-worst-speech-ever-we-ve-added-enough-new-oil-and-gas-pipeline-to-encircle-the-earth-e5e24a156910/

In the context of the death of all our futures and the extermination of a million species, Biden showing off his fucking gas guzzling car is an obscenity.

Regarding your other points:

Obama's presidency was a great failure. He failed to deliver anything positive of note. Of course, he was better than the incompetent and corrupt idiot Bush, and the delusional psychopath Trump, but that's the lowest bar in the world.

The ACA was a bandaid on a sucking chest wound, which was marginally better than what was there before, but still left the US with the most expensive healthcare in the world with some of the worst outcomes in the developed world.

And because Obama and Biden strongly believe that single payer is bad, that health coverage must be associated with a job, when the jobs collapsed, so did everyone's healthcare. In the middle of a pandemic.

If Obama had delivered anything for the poorest 50% of Americans there would be no Trump.

You say "championing issues affecting all Americans", I assume you mean championing segregation? https://www.nbcnews.com/news/nbcblk/joe-biden-didn-t-just-compromise-segregationists-he-fought-their-n1021626