Complex sentence: Methodism was never the faith of the majority of Torontonians but the faith played a very important role in the city, and Toronto had one of the, if not the, largest population of Methodists in the world.
Split into simpler sentences: Methodism was never the faith of the majority of Torontonians, yet it played a very important role in the city. In addition, Toronto had one of the largest (if not "the" largest) population of Methodists in the world.