Hi you are partially correct.Zarvin,
You are absolutely right in your reasoning that Pakistan would have profited if it would have backed a non-Pashtun entity and this entity would be ruling on the other side of the Durand line.
Do consider the possibility that Pakistan's leaders played a bad hand and backed the party that "could" eventually be inimical to Pakistan's interests!
If Ahmed Shah Massoud the Tajik was in power, we would've closed and sealed our borders with Afghanistan a long time ago, that is all we wanted. An unstable or prosperous Afghanistan is not our concern in all honesty, every country looks out for its own interests and ours was that this Durand line issue will cause us problems for centuries to come if it is not resolved, and resolved doesn't mean it being overlooked as the Taliban did, it means we have totally sealed and closed borders with them and only a Non-Pashtun element can provide us that.
However, after Zias death, Bhutto and Shariff were more interested in plundering our country then dealing with the fighting parties in Afghanistan--- Massoud started getting help from others and took Kabul, we couldn't allow that and started backing Hekmatyar the Pashtun, both were our proxies but they had started fighting for power after defeating the soviets, both were brutal and merciless criminals. That is when the Taliban emerged out of nowhere and took everyone by storm.


