Super Mario Run > Fire Emblem Heroes. Mario is actually a pretty fresh take on the formula, and it can get pretty challenging. Heroes is fun for 5 minutes at a time, but it's clearly aiming to hunt some whales.
I think you're right, seeing how they released Fire Emblem Heroes simultaneously on Android and iOS there aren't any excuses("yada, yada, so many different configs on android!")
Perhaps Nintendo struck a better deal with apple than their "we take 30% of your money" they use to have and had to go exclusive for a certain amount of time, because of that deal.