The patch workflow is smooth and just a great experience. It is vastly improved by some git aliases (which you can set up in your gitconfig), but is, in general, very smooth. It allows for local branches to a single upstream, topic tagging, and a reasonable learning curve. Much better than GH.
It would be very well served to have a web-based offering (like GitHub/Lab).
Can you explain what a "patch workflow" is and in what sense Github is not a "patch workflow"?
There's some confusion since some people associate "patch workflow" with an email-based workflow.
Email is one (very clunky) way of implementing such a workflow, there's other tools like Gerrit, Reviewable or Phabricator that are more friendly.
If I update the diff, does it become a new reviewable item, independent from the first version?
I've never worked at a large tech company but my understanding is that at e.g. google there is some sort of monorepo, so it would presumably zoom forwards while a commit is under review. Even so, why is it not a good thing to review the commit in an explicit location in the historical commit graph?
In fact, Gerrit is entirely based on Git and you can simply clone any given CL.