Bangla was just a sideshow. The PA's primary concern was defending the 'home country' or West Pakistan. The western front was about 1,000 miles and open to attack as most is rolling semi-desert. Major cities like Lahore are only 15 miles from Indian frontier and lay exposed. Don't also overlook the massive population resource disparity between Pakistan and India which of course feeds into all other resources. This infographic is for today but it gives you a idea. India is a union of I believe 30 [?] states. Just one, Utter Pradesh has the same population as Pakistan.
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Faced with such odds almost all the frontline units were deployed on the Western front. Other assets like most of the airforce also were deployed on the west. In fact questions had been raised as to why the east had miserably small force to which the strategy posited was "defence of the east lay in the west".
In fact the 55k number was elevated because in the previous 2 years the insurgents of the Mukhti Bahini [PKK in the Turkish context] supplied and trained by India was causing trouble. However because of the vast distance and Pakistan's very weak logistics reinforcements sent over to suppress the Mukhtos often went without their heavy equipment. The sea route was well over 3,000 miles making a V shape sailing along the Indian peninsula past Sri Lanka.
The reality was if PA could have contained the rebellion by Banglas it would have been a miracle. Let alone fending off a attack by India. A sober assessment woul;d have been to concede that PA could not hold 60 million people being fueled by India and let them go their way. But Pakistani ruling elite could not accept this and sadly we lost lot of brave men to a futile struggle and gave a soundbite to India which they still brag all these decades later.