Hard to say for certain as mobile gaming types are very diverse and the number of active games in every genre grows daily. Moreover, industry domination title will be different if you consider number of downloads and revenue, for example. By the number of downloads, hyper-casual action games lead the industry; however, the highest revenue belongs to RPGs, followed by strategy games.
Then there are mixes. One of the latest trends is the hyper-casual games mixed with idle mechanics, for example.