I understand why that point might be unsatisfying for some players. Someone else had expected Claw to fight Scourge at the climax of this arc, but this was never going to happen due to reasons that are probably a bit too meta.
Letting him leave was politically troublesome for anyone. If Pain wins, she would take him out to solidify her position. If he gets taken to the Passion Temple, Drishtya wouldn't want him alive, as she'd understand that his continued breathing would incite rebellion from his supporters, potentially having them call Claw's victory a fabricated story and generally making things more difficult down the line. Some players may have not seen it this way, but Drishtya is fundamentally a politician, and takes plenty of decisions that she herself dislikes through the game, because she understands they're the most pragmatic option.
And in any case, Claw defeating him wouldn't have been climactic for her. In her eyes, Scourge was never the big obstacle she had to overcome, just not the father she wished. It may be wrong of her to see it that way, but that's the only perspective she got to grow up with. Her tribe's conflict was always going to end in a tragedy, even if the good guys won.