Balkanized India that falls apart soon after independence would do it.
Another possibility is an India where a coup in the early years results in an almost comically inept, buffoonish government with shitty economics, incompetent military and a hated political regime. Think Idi Amin levels of buffoonery, Saddam's military incompetence and mixed with Great Leap Forward/Cultural Revolution levels of economic mismanagement and instability. In such a scenario, it is easy to visualize Pakistan in the 50s and 60s pulling ahead militarily and economically and staying there.
Of course, with a POD of 1947, this is very hard to imagine, but these two (Indian Balkanization or extreme incompetence) are the only two (slim) possibilities of how we can get a dominant Pakistan.