One thing that makes me skeptical is the lack of specific labels on the first two accuracy graphs. They just say it's a "log scale", without giving even a ballpark on the amount of time it took. Did the 80% accuracy test results take 10 seconds of compute? 10 minutes? 10 hours? 10 days? It's impossible to say with the data they've given us. The coding section indicates "ten hours to solve six challenging algorithmic…
The gist of the answer is hiding in plain sight: it took so long, on an exponential cost function, that they couldn't afford to explore any further.
The better their max demonstrated accuracy, the more impressive this report is. So why stop where they did? Why omit actual clock times or some cost proxy for it from the report? Obviously, it's because continuing was impractical and because those times/costs were already so large that they'd unfavorably affect how people respond to this report