I’m split on this. I used to agree with you but when I talked to internal users and customers, they really liked having a back button in the app. I would tell them the browser back button is there and we haven’t broken history so it should work to which they just often shrug and say they “just” prefer it.

My hypothesis is that they’ve had to deal with so many random web apps breaking the back button so that behaviour is no longer intuitive for them. So I don’t push back against in-app back buttons any more.

Bad UX that provides a functionality that otherwise isn't there at all is still better.