Durranis are more sophisticated and mild-mannered, while ghilzais are fiercer and far more traditional. Generally ghilzais were regarded as better warriors in the history but less civilized than durranis. Pashtunwali and pashtun culture is followed more strongly by ghilzais, even in north they are sticking to it while durranis would easily assimilate into dari population. Moreover ghilzais were nomads, portion of them still have nomadic lifestyle while durranis were always settled people.
Ghilzai-Durrani rivalry or enmity was noticeable in Mughal-Safavid wars. Durranis sided with Safavids while Ghilzais sided with Mughals. Ghilzais also aided Mughals in their campaigns against uzbeks during Shahjahan times While durranis were present in the courts of safavids since 16th century.
Kandhar became bone of contention between durranis and ghilzais. Safavid rulers obviously favoured durranis over ghilzais in case of kandhar but tides turned when Mirawais, a ghilzai chief of hotak branch captured kandhar from safavids in 1708. Ghilzais exiled durranis towards Herat. In 1719 ghilzais began to conquer sistan and in 1721 isfahan, capital of safavid empire, was captured by hotaki ghilzais.
In 1729 Nadir shah defeated ghilzais in iran and , as precautionary measure also defeated durranis of herat. Nadir shah won the support of durranis as well as tokhi branch of ghilzais who were bitter enemies of hotak branch of ghilzais who were still ruling kandhar. In 1738 nadir shah captured kandhar and handed it over to durranis, while hotaks were exiled to mashhad. The remaining branches of ghilzais were defeated by nadir shah one by one as far as kabul. India was actually invaded for the reason that some ghilzais had taken refuge there among mughals. In Nadir shah's victories against ghilzais, role of durranis was quite evident.
Ghilzais didnt support Ahmad shah abdali, or any durrani king or emir. At various points, ghilzais revolted against durrani rulers. When they revolted in the times of emir abdulal rehman, the iron king, large number of them were exiled to north. The nashar khan you mentioned, was chief of kharoti branch of ghilzais and they were exiled to kunduz in north by amir abdul rehman.
Ghilzais are not that great in number in Pakistan. Nasar branch of ghilzai, who were powindas, are settled in balochistan while there are some sulieman khels (another branch of ghilzais) in south waziristan. Lodhi tribes, are cousins of ghilzais, and are numerous in pakistan. Lodhi trribes includes niazis, marwats, kundis, dotanis, daulat khels, miankhels, sherwani, suris, prangis etc etc
There are African-Black people on coast of mekran, because they were bought as slaves by Balochs, the ones in karachi migrated from balochistan, when given freedom by their baloch masters due to great drought.