This GUI must have a pretty advanced versioning and rollback support, otherwise I can see one user borking the whole API with a bad change and nowwhere to check what happened.
Things would fail, rollback, and then the logs would have their errors truncated or something. I wasted so many days deploying botched releases from coworkers.
And the use of Phabricator at Uber was a nightmare. LLVM uses it correctly, IDK what Uber did but it was a PITA to do really anything.
Pair that with the siloed off teams where "every team is its own startup" mentality and you have constant fighting, power grabs, being blocked all the time, etc.
One one user talking own all APIs, the system has ability to skip unmountable APIs, but we catch it during user interactions with tons of test and validations.