I'm not Heroku's biggest fan, and haven't used it for more than a couple of one-off fiddles to play with the platform. But, my sympathy is going to them, because what I see coming from Rap Genius looks like classic blame-game. So a vendors documentation was unclear and your server sucked publicly for some time? Shameful. You didn't know about it because you expected your vendors to give you extra hand-holding? That's…
I'm having a hard time understanding your justification for your sympathy going to Heroku. RG is paying for PaaS from Heroku based on documentation, sales pitches, etc. They're also paying good money for the tools necessary to make business decisions based on data collected from that PaaS. Just given the realm of customer service, why wouldn't you expect "hand-holding" from your vendor? Why is it unreasonable to have…
And, if you're going to go public with your complaints, it's best to do so in an understated, fact based manner. In this case, Rap Genius comes off like a guy screaming at the waiter in a fancy restaurant. They may be displeased, they may even be right about the choucroutes en sel being salted cabbage; but lot's of people around think they're making an ass of themselves.