I'm not surprised how good true, dedicated cameras are. I think I could see a case for owning one, but you have to admit, a good smartphone camera, all things being considered is still a pretty decent thing. The convenience factor is of course of major significance. Still, if I knew that I was going to a special event or destination, and really, really wanted the best possible pictures, I could see owning a good dedicated camera.
Saying that, I would not want to spend more than about $500 on a dedicated camera, and for that money it would have to be noticeably better than any smartphone camera going to justify that price. After all, the only function it would perform is taking pictures/video, so for that money it better be well better than a smartphone. Otherwise, it wouldn't make any sense. If you have to spend closer to a $1000 on a dedicated camera, for example, to best the best smartphone, the point of diminishing return/marginality has to be viewed as considerable.
The smartphone offers the user quite a few tangible benefits/uses, including the camera, so a simple camera alone should not be nearly as expensive to best it at photography alone. IMO. I have no idea what dedicated cameras cost these days, I'll have to go look as I'm curious now.