He didn't do well in Detroit, Chicago, Philadelphia, or Cincinnati. Doesn't matter if it was Republican machines that brought Hoover to the top in those places, FDR still outperformed him in those places in 1932 and 1936.
Are we sure Catholics were a >50%, legitimate majority in enough of those counties to carry them for Smith in 1928?
I can't be 100% confident, but they probably were. 59% of Detroit was foreign born or 2nd generation in 1930, according to this chart. The "Canadians" were probably more Catholic than Protestant because Windsor is heavily Catholic. Maybe a lot of the immigrants were too young or illiterate to vote, but Grover Cleveland was still able to win Wayne County.
If that's what Detroit's demographics looked like, I think Chicago would have even less favorable demographics for Hoover.
Cincinnati was also probably majority Catholic, as there are more Catholics than Protestants in Hamilton County even today according to the Census, and it didn't have the high black population that it does today.
Philadelphia's demographics might have been just favorable enough for Hoover to squeak a victory.
