My understanding is that mobile is so over-saturated that its the equivalent of gambling. I have no proof other than my limited experience in the industry, but Steam tends to be more of a meritocracy. If you make a good game in a genre people want to play, you have a decent chance of making some good money. There are people waiting and wanting those types of games. They'll forgive the lack of 3D graphics or fancy voice overs, etc if the game itself is solid. The top sellers in 2014 were almost all non-AAA titles.
With mobile, your marketing budget is more important than your game. Anyone can code a ad-driven clone of $popular_game, like your friend did. If anything, mobile is a lesson in attracting the wrong kind of developers (quick cash kiddies making clones) and a lesson in how poorly organized and run the various App stores are. Not to mention, how unsophisticated the mobile buyer is. Its grandma looking for a distraction, not the next Half-Life.