Ultimately I think its poetic, I feel like this all comes back to what we learned long ago with Usogui's relationships as spoken by Yakou. His team was all prepared to bleed for Usogui and his dream (and many of them have suffered serious injuries or death), and Baku was prepared to bleed to pay the price as well. Fukurou and Lalo were not prepared to bleed for each other, and in a way, everyone in Ideal was prepared to sacrifice for their own goals, but not necessarily Lalo's.
Fukurou really didn't do anything wrong. He completed his duties perfectly, making the best hands each round outside of the flub in Round 4, and had very little information other than what be could deduce on his own. But elder Nowa does mention that he made a mistake. How the author wants us to interpret this is a bit unclear at the moment, but its not a big obvious mistake like making a bad hand. Fukurou seems to believe so as well; when the pain moved in to punish him on the final round, Fukurou seems to be expecting it and resigned to whatever fate he will endure. I think he understood that there must have been a deeper meaning to Hal's invalid hand, but could not figure it out. Perhaps Fukurou and Lalo could have sniffed out the situation by getting to see that Hal made a "mistake" and Lalo's 1 bios scan, but ultimately Usogui and Hal's teamwork was far superior and the cracked regulator mindgame was too much. Lalo didn't think hard enough about why Usogui played 26 before 25.
Count me among those that think it'd be fitting for the final pain to be drowning. Didn't even consider that, I figured it'd be beheading or crushed or something.