First off just want to say this has been my favorite article I've read since joining steemit and you got a hard follow from me @infovore!!! It's refreshing to see an outlook on this industry because a lot of people don't really understand this niche.
Early on when I first found success with FB ads there certain styles of ads I was running that contained viral content, and Facebook's algorithm couldn't really track the conversions like they do now. I'd have ads go so viral they would reach over 1,000,000M people and have engagement through the roof. Most ads had over 500,000 likes, etc.
Facebook's Ads Manager (which is their internal interface where you manage paid ads, etc) has now drastically changed. Don't get me wrong, it's still a super powerful source and my main revenue driver but to experience the changes and see it first hand with serious money on the line is eye opening.
You can still find ways for cheap conversions and be super lucrative, but need to know what you're doing. You need to watch your ads like a hawk because at the end of the day you set the budget and FACEBOOK technically can spend that budget however they want once your ad is approved.