It's not a straw man at all as products with Unity aren't making any effort to appear native to the platform they're running on.
Unity is also notoriously painful when it comes to 2D UI style work as well, which is why there's a tools ecosystem around it just to deal with that problem.
Games are way different segment. In a game you would like to impress person with non standard interface. In fact a game running on standard UI looks cheap and is a signal of design failure / low budget.
While the applications are other way around. New customers do not want to spend more than a minute to get familized with the interface. Moreover, your custom UI interface will be competing with Apple/Google designer's budget.
Unity is also notoriously painful when it comes to 2D UI style work as well, which is why there's a tools ecosystem around it just to deal with that problem.