That may be true but Leeds are undoubtedly a much bigger club than City. They have a national fan base. In my experience the following clubs have fans across the whole of the country:
Everton
Leeds
Newcastle
Villa
Then you've got United, Liverpool, Spurs, Chelsea and Arsenal who have an international fanbase.
City realistically are on par with Sunderland, Stoke, Sheffield Wednesday, Coventry etc. I've never met anyone who supports these clubs and isn't from the local area. Although I think a lot of kids 12 and under support City these days so maybe that'll change in the next decade or so.