The extra weight would compare to the extra weight of some of the "bull barrels" out there. Extra strength can't be denied, even if perceived as unnecessary - I sure would want that SS receiver if I were planning on dropping a Lightning Link or RDIAS in it, or even a belt-fed upper. The little bit of extra weight would be a benefit in .308 AR's
It's not just that the "extra strength" is perceived
as unnecessary, it ACTUALLY is unnecessary.
The weight of a bull barrel isn't analogous to the weight of a stainless receiver, vs. an aluminum receiver.
Fact is, in my humble opinion, there just isn't any cogent reason to craft an AR receiver out of stainless steel.