India could not even fight LTTE which India funded, trained, and armed. IPKR had 70,000 soldiers in northern Sri-Lanka which is a much smaller geography then Bangladesh, yet it failed miserably.
Actually India trained mostly Mujib bahini, which almost never took part in actual warfare. This Mujib Bahini later became much hated "Rokhi Bahini" following independence.
India did provide small arms, some training, and shelter to a few million people.
The East Bengal Regiment put up fight especially in the Chittagong area with their own weapons starting from the early days. They lost 1,000s of their own, but they fought as they were trained to do. Most fighting were done by the these military folks and the young men from the rural areas.
Read this book, written by a freedom fighter. This man has a Ph.D and taught at University in USA.