Also, your Google ad is significantly better looking than your Facebook ad, and is also much more likely to be seen while people are on their mobile phones.
Facebook supports conversion pixels as well, so conversions through his signup flow could have been measured. Instead we just get a vague disappointment in WoW signups
So I spent around the same time setting up the Facebook campaign as the AdMob one (about an hour each, including the time to make the graphic), and for the time/$ spend, the AdMob campaign trounced the FB one.
In terms of conversion tracking, it was quite unscientific, true. But basically, I can track the number of new players of the game per day. Normally I get a pretty steady flow just from the Play Store. With the FB campaign running, there was no significant uptick in signups, but with the AdMob one running, the uptick in signups was immediately clear.
I didn't actually know it's possible to target mobile only with FB campaigns, and so I'll definitely be giving that a go.
Anyway, my point with the post was just that for someone on a tight budget, with not a lot of mental bandwidth to spare for tracking ad conversions, AdMob was just way better value for me.
However what the OP did is sort of life-time-value (LTV) analysis which in the long run might give a better indicator on return-on-ad-spend. Post-install tracking is available now via various 3rd party tracking solutions.
It does involve more up-front work on an app developer - i.e. find all the important metrics in the app that is relevant (sign-ups, various activities like virtual good purchases etc...), and track these metrics over time.
There are quite a few flaws in the OP which most of the comments here have captured, and provided remedies to fix them, so I won't repeat them here. I look forward to the follow up here.
Disclaimer: an ex-Admob engineer + currently working in a mobile ad startup.