I agree that an adversarial tone is not advisable for multiple reasons. I have seen a couple of articles on this topic where the engineer comes across as downright rude. I think this particular article (mostly) avoided this trap and recognized that while there are legitimate issues with the way recruiters approach engineers, this is still ultimately a good problem to have. Being in demand is great, but the tides can turn quickly in any profession (see: lawyers). I think it's perfectly appropriate to be able to point out issues with recruiting, but ideally with a sense of humility and appreciation for the opportunities that one has -- this article does that for the most part.
I agree that it may be unrealistic to expect fully functioning products out of a three day hackathon, but I am continually impressed by the amount that people accomplish in such a short period of time. Extreme time constraints can often be a useful tool to break conventional thinking and prompt disruptive solutions.
Here's two suggestions that might produce a more focused outcome and reduce wasted effort:
1) Engage key stakeholders throughout the hackathon - so that a deeper understanding of their problems is reflected in the hacked solutions
2) Offer an "overtime" session for those who are interested in working with the stakeholder over an extended period (a few weeks or possibly months) to refine the solution