I think this is wrong. These games have strong invite-friend mechanisms and have high retention. That's why they are popular in the first place. No source at hand though.
Whales only play one game at a time.
"A service launching this week will tell you that Machine Zone is currently spending somewhere around $12 per user with AdColony, InMobi, and Unity Ads, up to $20 per user with Vungle, and between $2 and $30 per user with Chartboost."
http://venturebeat.com/2015/08/12/this-service-tells-you-wha...
GoW has very low retention. Users who stick around in GoW are the kind of people who like to spend a lot of money to feel empowered. But, finding and keeping those people is very expensive because it involves churning through a whole lot of users who aren't like that.