Regarding Gazelle, yes, the CI would break early if it detected a none porcelain repo after running Gazelle itself. I think others may have configured their editors, but for me the occasional 30+s run time (and as mentioned in some workflows 3-4 mins) on file save - plus the already creaking VSCode plugins was too much to bear.
Was it 3-4 minutes when updating a single file? Or only running over the whole repo?
It's when you have multiple languages and want to be able to build/test only what has changed that you need a Blaze-alike.
With regards to Gazelle: is it intended to be run every build, on every file? Or is it intended to be hooked into your editor, and run on save to update your BUILD files as you go? At Google, I used the latter kind of tool, and it worked just fine. If it missed something, you'd notice when the CI system failed to build/test your change.