I consider this "strongest tribe" idea to be very mislead. It's not about strength or reliability. It's about threat value instead. There's little to no booty (the classic tribal warfare motivator) to gain in the Afghanistan conflict, therefore choosing sides is either about power (relevant only to a minority) or security.

The "strongest tribe" concept doesn't pass my plausibility check, a "most threatening power" concept could do so.
Excuse me, but didn't the Soviets try the terror through mass murder method in Afghanistan already? They killed something like 1.5 million Afghans and created 3 million refugees out of a prewar population of 15 million. Does anyone here believe that Afghan villagers did not live in fear of Soviet bombers and artillery? Certainly enough Pashtuns in the south were terrified enough to flood Pakistan with 2 million refugees.

This did not help their security problem in the countryside nor did it kill resistance to DRA rule. By 1986 they had already decided to withdraw from the country, despite the fact that the first Stinger missiles had not yet arrived.

Moreover, can someone please tell me how a foreign occupation that bases its control on terror can create a semi-stable native regime once it leaves? One not based on hopes and dreams?