The big fights over railroad rate fixing were in the late 1800’s. The National Grange among others was engaged in fights over that. And Carnegie himself had extensive railroad holdings. He stood to benefit either way.
Pittsburgh is a nice place, but it would not have become so opulently wealthy if the fix had not been in.
The Grange won that battle in 1887 with passage of the Interstate Commerce Act which ended discriminating rail rates. All rates had to be published and no difference in pricing was allowed between shippers.