http://appshopper.com/bestsellers/gros/?device=iphone
Look at what the top grossing games are.
Candy Crush Saga, Farm Heroes Saga, and Pet Rescue Saga are derived from King's games on Facebook like Bubble Witch Saga.
Hay Day is basically Farmville, and FarmVille 2: Country Escape is also a top grossing mobile title.
Big Fish Casino and all the other gambling titles are like Facebook gambling games.
The Simpsons: Tapped Out is essentially a Facebook town builder.
Underworld Empire is effectively Kabam's The Godfather game from Facebook, but without the license.
Game of War - Fire Age is like Travian, which is (was?) a very popular social browser town-building-and-combat game in Europe. The Hobbit is basically the same thing.
There are a few new additions like Clash of Clans and Boom Beach which are a bit too complicated to run in a browser without a Unity plugin, which would limit their appeal on Facebook, but doesn't stop them on mobile. They're very similar games though to the other types of hits.
Then there are things like Marvel War of Heroes which is derived from the type of social game that dominated Japanese mobile games when they were feature phones.
And on that note, feature phone game revenue was also in the multibillions in Japan for many years. They're not "fresh meat". A lot of the top grossing games in Japan are still the exact same kind that have been top grossing games for over half a decade.