No, the Quick Mask function is not enough!
Working with Masks is essential for many functions but this means not only to create Masks, e.g. by using the Quick Mask function.
It is also essential to Edit Masks, that means modifying existing masks after creation, later on again.
Use Case:
Create a mask to mask a pixel/bitmap layer
(do something else...)
Select in Layers window the existing mask (as created some time before) and select "Edit Mask"
Try to modify the mask in context with the background layer (where the mask is applied on)
-> Here we still need the "Overlay function", so that you can modify the mask in context with the background which is currently not visible!
As I wrote before for "Quick Mask" and "Refine Mask…" the Overlay is working but "Edit Mask" is a different use case, for that the Overlay is not working.
e.g. if you want to use the "Paint Brush Tool" to add black or white areas into the existing mask in context with the background layer.