> whereas the teams are allowed to bring a 25-page PDF
This is where I see the biggest issue. LLMs are first-and-foremost text compression algorithms. They have a compressed version of a very good chunk of human writing.
After being text compression engines, LLMs are really good at interpolating text based on the generalization induced by the lossy compression.
What this result really tells us is that, given a reasonably well compressed corpus of human knowledge, the ICPC can be view as an interpolation task.