To sum up, these benefits came from losing an arm this time.
First, it won the goodwill of Fish-Man Island, laying the groundwork for Poseidon in the future.
Second, it won the goodwill of the Revolutionary Army, laying the groundwork for the future (secret).
Third, it won Fisher Tiger's goodwill, using this incident to clear the protagonist's name in the future. (The reason the protagonist guessed Fisher Tiger could survive was that he knew someone like Dragon would not act without a certain degree of confidence.)
Fourth, it gave the Five Elders the impression that he was caught between his mission and his own principles. (That better fits the protagonist's characterization. Otherwise, they would suspect that he was secretly scheming.)
(This is actually the most crucial point. If someone who prides himself on being just made no response at all in a situation like this and completed his mission perfectly, then in the eyes of the Five Elders, was the protagonist merely hiding his dissatisfaction, or was his entire persona fabricated? Would they still dare to use someone so deep and calculating? The same applied to the public. With even a little thought, the implications became terrifying.)
(Looking at it in greater detail, if the protagonist did not capture Fisher Tiger, Fish-Man Island would be destroyed and the later plot would collapse. If he captured Fisher Tiger and pleaded with the Five Elders, he would no longer be valued and the plot would collapse. If he captured Fisher Tiger, completed his mission perfectly, and made no response at all, his characterization would collapse. From this perspective, the protagonist had to react so strongly!)
Fifth, it left him with a "weakness" that would make it easier to strike at others covertly in the future. (That did not mean he had already