The problem wasn't that queuing delay was impossible to detect. The problem was that the documentation described a specific load balancing setup that would have guaranteed better performance per dyno, and that setup was not in fact what was being delivered. It was clearly a material misrepresentation, and in any other service context would constitute a deceptive trade practice. That Heroku is being defended at all is a testament to the goodwill they've built up in the tech community, but it doesn't change the fact that they misrepresented their service, even if it was negligence rather than malice.