Boros could tell which of the three parties on the battlefield would have the quickest and biggest effect on the overall battle without thinking.
It was without a doubt Goro. He was the strongest fighter on their side. As soon as he won his battle, he could steamroll the other two sides of the battlefield.
The four warriors were injured and exhausted. They would have trouble facing Ulminer Go. Alzara wasn't more than superficially injured, but she was exhausted.
Based on her attitude the last couple of days, she also might not be inclined to help the others. She might decide to sit back down or leave the area as soon as she won her fight.
If Borso wanted the best odds for them all to win and survive, he had to separate Goro from Ulminer somehow and let the bear into the other fights.
But that was where the problem appeared.
How was Borso, the weakest in the desert, supposed to do something to Ulminer Go, one of the strongest?
No.