You make it sound as if the 70 million Bangladeshis were some kind of were trained well-coordinated and well supplied army.
There is not a single instance/war in post WW2 where guerrilla or unconventional militia have won against a conventional military on their own.
Its true, without Bangladeshi support, India couldn't have won the war so soon.
Same way there are elements of military genius which ended the war so soon.
what i know is that the shear stupidity of the then pakistani regime was the biggest contributor to the collapse