I think it was more to do with City fans wanting to reinforce that we are / were the only club in Manchester and wanting the city's full name in use. "Man U" was a term coined by out of town rags to avoid having to admit they supported a team from the town they had no connection with. It gentrified their club.
I recall the night Kevin Keegan was introduced to supporters club officials on his first day and he said Man City a few times and someone asked him to call us Manchester City as that is our name.... "we are not like Man U. We are from Manchester"
And now our website is ManCity.com and the MEN repeatedly call the rags Manchester United and us as Man City even in the same headline title
I would completely endorse your facts on this post Phil.
The first time I heard the name Man U mentioned was by my nephew (on the wife's side I may add,no rags on my side of the family).
He stayed overnight at our house in Moston to attend the funeral of my wife's aunt/ his great aunt in 1992.
He wanted to go to the club shop at OT to buy the usual stuff,and started going on about how he was a Man U fan.
He was a typical glory hunter, born in Manchester but moved to Devon at 3 years old.
And had been to OT twice ,both times as a child.
All the local rags I knew (school and work) always referred to us as City, and of course they were called United by us local City fans.
Manchester never came into it,because we all came from Manchester or it's surrounding towns.
It's definitely the out of town rags who downgraded the Manchester (United/City) into Man U/City.
All I can utter in response is
"Fuck off back to London/Devon/Surrey/Ulster " etc.