Mistakes were made by both sides political mistakes aside. Mujeeb could have been writing but his 5 points were enough to strengthen this divide foundation of which was laid in Agartala conspericy.
As for military I think that hard line bangali are more to be blamed. There minds were poisoned by Mujeeb ur Rahman to the extend that they lifted armed against their own Army. On the other hand the sole mistake of military crack down was to prevent splitting of Pakistan. In any situation any country in the world would do everything in order to keep its ones.