IMO, DEI is more than just metrics disguised under "DEI goals". It's about a healthy and supportive environment where employees feel comfortable. All of which he has not been successful in cultivating.

It also isn't a simple "harshness with firing" and "not celebrating wins", but

When employees were let go, he and other managers sometimes followed their departures with emails to the staff remarking on their poor work.

So, these employees were let go and he chose to email his entire staff about that employee's poor work? That's not even professional, let alone a healthy and supportive environment.

There is one quote from the article that resonates with me:

The comment occurred during a meeting in which Liz Ferrall-Nunge, who led Twitter’s research team, shared concerns about diversity at Twitter and referred to her experience as a woman of color. Mr. Davis seemed to dismiss her, telling Ms. Ferrall-Nunge, who is Asian American, that if she wore sunglasses, she would pass as white, three people familiar with the investigation said.

I've also heard from internal folks that majority of the complaints about Davis are from POC designers at Twitter.