Strange to hear that perfect pixel is dead. As a frontend developer, I always pay attention to what icons I use. Usually, any system has no more than three standard icon sizes. For example, in my current place of work there are two icon sizes, 16x16px for icons inside buttons and 24x24px for lists of panels and other things. If the line is curved, there can be no hit to the pixel. But if the line is straight, it should be exactly on the grid. If this is not the case, it looks unprofessional. For example, customers often open our system on huge 70" TVs with 4K resolution. All lines that are blurred-immediately catches the eye.
Moreover, the custom scale can almost always be taken into account when creating an icon. For example, if the user sets the screen scale to 150%, the physical size of 24x24 will turn into 36x36. If you make the icon lines 2px thick, then at a scale of 150px the line will become 3px thick and will still fit nicely into the grid.
Perhaps the graphic designer can ignore the perfect pixel, but the interface designer can never. If it's a good designer.