The largest browser in the world does what I'm describing with much success. On the other hand, Firefox used to be more styled toward the operating system, and has also moved away from that. Even then, its default widgets are styled like the system, which has led to inconsistent and annoying styling, especially on Linux. I remember having some specific GTK styles on my computer years ago that made certain FF pages without CSS styling nearly unreadable because of FF respecting GTK's styling of textboxes and buttons. I actually still have at least one screenshot of this I took when it happened because it looked so bad.
I'm not saying everyone should roll their own custom application style, I'm saying toolkits should make very well thought out styling decisions and then use those on all platforms they support. Some OS-influenced styling can still happen, like the OS's dark mode setting. But I would be very surprised if the average computer user had any preference for whether an application looked like his or her OS.
