Niazi had to be jelly legged.except, that Sam Manekshaw, never even looked for Unilateral Surrender, but rather a Ceasefire. It was General Jacob who bulldozed a jelly legged Niazi to secure the surrender. Until JFR Jacob, was already in dhaka, Neither Gen JS Arora, nor FM Manekshaw knew about the instrument of surrender. So the khayai pullaav deal, Deal Behlane ke liye theek hai.
He had no political support from Islamabad. He was on his own.
But he did great under those situations. With India sitting in the middle, cutting off supplies, the Pakistani army did great.
If India was winning that much, they would not have signed any surrender deal, rather killed as many Pakistani soldiers as possible.
So by manikshssw own admission, the Pakistani army did fight bravely and indan army made a deal to avoid bloodshed of Indian soldiers. Likewise Niazi was not a big fan of fighting and killed some 13 year old ", Bangla babu" and found surrender the better option.