This is a complicated topic. To me the ability to hold a coherent (not necessarily still for reasons I won't elaborate on fully to keep this message somewhat short but essentially there is a large kinesthetic component that I suspect a very large percentage of people, myself included, rely on to visualize) 'image' in the minds eye is the measure of hyperphantasia. But 'image' is the wrong word because the 'image' we see in our mind is probably more of a rational reconstruction in our mind spurred by some sort of impression that first formed the memory that the image is reconstructed from. Aristotle wrote about this and more in "On Memory and Reminiscence", I am not correctly conveying the idea.
If you could accurately form an image of a realistic face in your mind then barring some sort of motor issue you would I argue by definition be able to draw it on paper by using the image in your mind as a reference (obviously the technical skill of using a pencil to dutifully create lines which entirely match what is attempted might be lacking and it might be a poor picture in a technical sense but I think it would still be recognizable as a realistic face). The difficulty in drawing a realistic face is that you don't actually know what one looks like, or, more accurately, you have the ability to recognize what a realistic face in general should look like (perhaps due to some inbuilt neural circuitry) but you don't have the ability to recall it in all of its detail. Because you can't recall it you can't form that image in your mind. Anyone who can't draw a realistic face doesn't actually know what a realistic face actually looks like, they can only recognize it. I don't think this would be a controversial view among talented artists for instance because many well regarded treatises on the subject of drawing essentially put forward this idea.
I guess what I am trying to say is that your ability to visualize a face is probably not much better or worse than your ability to visualize any other object of similar complexity except that you would be much better at recognizing that the face you visualize isn't very accurate. If you weren't able to recognize that it wasn't accurate you wouldn't have critiqued it and if you did you wouldn't have remembered the critique anyways.
To close by detracting from everything I have just written: You can also draw a very convincing face by memorizing a complex set of rules that doesn't rely at all on visualizing anything so who is to say that isn't the thing that happens when someone draws a realistic face which puts this whole business of visualization into some doubt
If you could accurately form an image of a realistic face in your mind then barring some sort of motor issue you would I argue by definition be able to draw it on paper by using the image in your mind as a reference (obviously the technical skill of using a pencil to dutifully create lines which entirely match what is attempted might be lacking and it might be a poor picture in a technical sense but I think it would still be recognizable as a realistic face). The difficulty in drawing a realistic face is that you don't actually know what one looks like, or, more accurately, you have the ability to recognize what a realistic face in general should look like (perhaps due to some inbuilt neural circuitry) but you don't have the ability to recall it in all of its detail. Because you can't recall it you can't form that image in your mind. Anyone who can't draw a realistic face doesn't actually know what a realistic face actually looks like, they can only recognize it. I don't think this would be a controversial view among talented artists for instance because many well regarded treatises on the subject of drawing essentially put forward this idea.
I guess what I am trying to say is that your ability to visualize a face is probably not much better or worse than your ability to visualize any other object of similar complexity except that you would be much better at recognizing that the face you visualize isn't very accurate. If you weren't able to recognize that it wasn't accurate you wouldn't have critiqued it and if you did you wouldn't have remembered the critique anyways.
To close by detracting from everything I have just written: You can also draw a very convincing face by memorizing a complex set of rules that doesn't rely at all on visualizing anything so who is to say that isn't the thing that happens when someone draws a realistic face which puts this whole business of visualization into some doubt