Hi outsider,
GSD is the best we have ;-)
It basically represents the best possible 'resolution' you can achieve, which does not say much about the quality of the images or resulting model.
For example, even though the GSD is let's say 5mm/pixel, it does not mean that you can properly resolve or identify features that are even 2cm big in your imagery or model. The ability to identify and model such features depends on the image quality, which (as you pointed out) is controlled by many factors such as camera settings, quality of lens, dynamic range of sensor, image blur, .....
Regards,
SAV