To an extent you are right, it was a tribal confederacy held together by strong personality and leadership of Abdali , his successors were not that talented and competent. Still the main factor in decline of empire was the civil war and loose central authority. By 1798 Afghan rule on Punjab was nominal and Sikh misals were the practical rulers, the civil war in Afghanistan triggered the forward policy of Sikhs and the first Afghan stronghold in Punjab, Kasur, fell in 1807 AD because Sadozai vs Barakzai conflict was going on and none of the side came to the aid. Abdali himself never had full control over his own domain but he was capable of suppressing any revolt with his military experience, his successors, the Sadozais ,were unable to properly administer such a large empire in the absence of proper administration and proper system. Abdali crushed every Sikh force he encountered but he failed to find the solution for ending the Sikh insurgency. Durranis were newbies, they had no experience of administration like Mughals.
