It can be done, but not by the typical person who enters the contest. From what I've seen, most entrants have not written anything that long previously and are using the contest to motivate themselves to do it, which is a red flag in itself. It requires experience and genuine interest in and excitement for the material to write anything coherent in one month or less. I completely disagree with the idea of simply hammering out whatever comes in the moment and worrying about editing later. Yes, sometimes stories take unexpected turns, but without a solid outline those turns become random, desperate attempts to make the story cohesive.
I wrote the first draft of my third novel in six weeks. My experience writing the first two had a lot to do with that, as did the fact I started on a random day and had not set a deadline, so I was under no pressure to finish at a certain time. As it turns out, my outline was not the full story but only the first two acts. The big end reveal turned out to be the setup for an act three I had never considered, but because I had a clear idea of how to start and where I needed to end up, I was able to flesh out the story and ended up with something surprising and quite different for science fiction. Had I tried to write that book for NaNoWriMo it would have been incomplete and so sloppy I most likely would have trashed it.
New writers need to relax and focus on telling their stories, not worry about meeting deadlines. If they have another idea and want to test themselves after having a few novels under their belt, that's a different scenario, ut by then we're usually beyond the need for such tests.
Sadly, we will just have to wait for AI to get better. Some day, we will have reliable division between the popular mass-market garbage and things worth reading. Alas, that day remains far in the future.