I don't agree with the "reciever is a receiver" statement. Lets set aside the forged vs billet and look at forged 7075 receiver sets. The most obvious differences are in the finish. Three types of finish used are:
Hardcoat Anodize, or "Hard anodic coating" this is called "MIL-A-8625, Type III, Class 1 or Class 2" This anodic coating has a thickness 0.002” ± 0.0002, it has a dye added for the finish color.
Sulfuric Anodize, this is "MIL-A-8625 Type II, Class 1 or Class 2". This is a Anodic film on aluminum, dye is used for color.
Hardcoat Anodize w/Teflon this is "MIL-A-63576, Type I"
Type II = Sulfuric Acid Anodize
Type III = Sulfuric Acid Hardcoat Anodize
Class 1 = Non-dyed Coatings
Class 2 = Dyed Coatings (color to be specified)
Everything today is Class 2, dye added. Type III well cost a bit more as well the Teflon additive.
Manufacturers should list the type and class of finish.
The added dye is the reason we see different finish colors.
Now lets add lowers that can except ambi controls or 45* safety selectors. Compare mag well bevels.
Even more difference with billet receiver sets.
A "receiver is a receiver" is not always a receiver.