I think you're right so once again the answer on whether to use a hamburger icon for a menu is: "it depends".

We use it within our app because it makes the most sense and we have more functions than can easily fit onto a tab bar. We also have a suite of functions wrapped in a single app opposed to separate applications so having a larger menu of functions is the wiser choice. We also host a subscription-based service with tons of training for our customers so there's little need to expose them to other features of our application. We aren't competing for eyeballs or views or whatever so there are lots of reasons that it works for our organization where it might not work for others.

I believe it's a completely valid UI pattern with pros and cons just like any other - it'll work for some people and won't work for others. Designers really just need to understand the potential issues and be able to justify the rationale of their decision for or against. (Edited for clarity)