If it's high pay you're after then you'll just have to be good at whatever it is you do. The senior devs for any field get paid way better than the beginners/freshers.
Having said that, on average some fields are paid higher than others. Data science is definitely hot here in India right now, and not as many people are in it. As you noticed, iOS is also a highly sought after skill these days, again probably because not as many people are in it. Also, if you want to be where the future is going I have to urge you to check out React Native development and JavaScript development in general.
Cheers :)