Any efficiencies you are seeing will be refactored and stretched out as any business cannot afford to carry fat if they want maximum profit and competitive edge (price).
This whole inconvenience of a friend going to the bathroom is an incredibly weak argument for foregoing the tradition and ceremony of interacting with a person who will provide you with a meal. If you want to live in a McWorld where every step of your dining experience is as sterile, efficient, and touch free as possible then I am sad for you. That's not what a meal with friends and family means to me, it's not just about eating for sustenance.
Why do you draw the line at taking payment?
Not around here, no. Was out eating yesterday. That place we went to has the exact same number of wait staff as before QR codes, the difference is only that they're not exhausted, they are not stressed when interacting with us (showing us the table, bringing food, checking in on us if we need something else, etc). We don't have to wait for them to get the bill or to pay. The overall atmosphere is much more relaxed now. And yes the other places I visit also keep the same number of staff as before, as far as I can tell.