I agree with your first paragraph, but democrats do not seem organized enough to choose someone else, you will just dilute your vote and argue more with whoever you choose next.
And at the end of the day, POTUS is still not the most powerful human being in the world, that's an illusion. There's still a congress and military that say "no" to some of their desires. Billionaires who control thousands of jobs and the lives of millions of people too. There are warlords out there with the weapons and soldiers under their wing, who listen to him, not the POTUS. So on and so forth; and given this, I still prefer a cadaver over Trump, but sure, democrats can do better, but I feel like you might end diluting your vote if you don't choose the right person, and judging by the comments, nobody seems to be able to decide who it should be, not even the kind of person s/he has to be