It wasn't just the audience that thought so; even Yoze felt that it was better for Darwin to lose this battle than continue fighting. Simply because the pressure that he felt coming from Gray's new body was a little stronger than the pressure, he felt when he had previously fought the Leopard demon.
Even if Gray couldn't manipulate his spiritual energy to the same level as the Leopard demon, Yoze didn't doubt that the physical abilities that Gray now processed were far higher than what he had shown before. Not to mention that Gray's transformation was bound to have some special abilities that should make it impossible for someone like Darwin to win.
In his eyes, there was nothing but death for Darwin if he tried to continue the battle. Unfortunately, regardless of what Yoze and the immortal cultivators thought was the best path for Darwin, it seemed that Gray's transformation utterly paralyzed him.