I would not over-read into that doc. In practice, the only missing stuff are extreme edge cases of the type that is actually not consistent between other implementations of bash.
In practice it works great. I haven't seen a failed command in a while
Counter anecdote: As a Google engineer it always seemed like Edge implemented the sparsest possible version of the web platform to make major Google products work–and literally nothing else. That works to launch the browser, but then basically any product change runs a chance to no longer fall into that sparse subset and break in a browser. If Edge had implemented a more robust set of features, it would have massively improved compatibility down the road.