When Bizarre Blade brought up the League's agreement, Brony finally decided to compromise!
That way, although Brony had deprived Bizarre Blade and his party of the opportunity to obtain the treasure, there was no way for him to avoid Bizarre Blade using the identity of "party member" to stake an advanced claim on a portion of the loot.
Furthermore…
The two Hall of Heroes members on Bizarre Blade's side had also joined Brony's team. While the portion that was to be allocated to the three individuals may not have been very large, it made the prideful Brony uncomfortable and uneasy in his heart. He felt like he got the short end of the stick in their dispute. Bizarre Blade may have become a member of his team, but it did not mean that Bizarre Blade's three-member team had to adhere to his instructions. The Three Great League's pact did not cover such a situation.