I get what you're doing and why, but you could've avoided some of the pushback that's happening just by not pointing a finger or mentioning Heroku. So instead of "we can only run good code and yours isn't," make it more like "gee whiz, you have it doing an in-memory sort of 189k rows! Is that what you intended? Because that's really an edge case in our world?"
A friend of mine once said, "a customer will defend his bad decision to the death if you point it out to him."