Is the source of your statements work experience? If it is, I'd like to work where you do. I find it very dangerous that some people really believe what you wrote is the universal truth.
Because it is. Developers who don't test their code once don't get hired after an internship.
Once you witness it in practice, it makes sense, even if it doesn't make it any better.
No, it doesn't. It goes against the very first lesson taught in every basic beginner coding class. Test your shit, you get nothing out of sending in code you have no idea even works, especially when you are just adding a feature onto a program you were just introduced to.
This lets them very quickly finish their tasks
Except they don't. They are extending the required time and pushing deadlines by constantly having to have someone else recreate and report basic bugs. Then bugs with specific causes will never be fixed, just requiring more manpower and adding more crunch for later.
If the progress is not properly assessed and the supervisors don't see the relationship between the initial task and the endless fixes, people can get away with such an approach, or may not even realize how inefficient they do their job.
Sorry to hear that you had literal children fresh from high school with zero coding experience as supervisors.
The next step is to imagine what happens if the manual testing doesn't cover the feature at all, for one reason or another...
Yeah, would love to know what reason or another they would not test the only feature the programmer was responsible for.
Quality control on all levels is still a massive issue for a lot of reasons, one being that writing the sufficient automated tests, despite all the available tools and libraries, tends to consume more resources than the features' development itself, and it's hard to prove how much work doesn't have to be done later thanks to them. Especially to people with little idea about software development.
Not remotely true in game development, especially when working with a well established game engine. Not testing will always take longer than simply testing the feature, not testing just adds more work for the developer in the long run.