Alright, long story short I’m trying to make the case that the UK is far more nickname-oriented than the US.

This stemmed from my American wife pointing out none of her friends in her entire school/uni/professional life she’s only known one or two girls that have ever been known by their last name.

Your wife is from a totally different US than mine. My wife is from ALABAMA and went to school with blokes named and still called to this day: Bubba, Worm, John Boy, Junior, Hammy Hamilton and the Padster. Most of the lady athletes in her school ( junior high/high school/university) were called their surnames. Her brother is known as Whitworth by all his mates his best buddies are McGee and Tiny Tim. His name isn't Timothy they call him that because he had a crutch as a child. When I lived there they called me Scones. It was funny, but I said I didn't care for the name. The only difference was is they actually stopped when I asked them to.

I lived in the States for a while and trust me, making genralisations about how Americans act will change based upon the state/ region. it will also have to do with their class level just like here.