I dont think that is true. Yousuf is not the best captain but because of the desi way, there is no other option after Younis Khan than Yousuf for captain otherwise there would have been more unharmony like it was under Shoaib Malik. Imran Farhat has a much bigger source for his inclusion, his father in law is part of the PCB Selection Committee under Iqbal Qasim (Mohammad Ilyas | Pakistan Cricket | Cricket Players and Officials | Cricinfo.com).
There is no indication that Yousuf asked for Sami. It was said that the tour management was asking for reinforcement in the bowling department, so they both (Selection committee and tour management) probably decided to get Sami. Yousuf is not that influential that the selectors will listen to him.
Yousuf is just a bad captain but unfortunately, being Pakistan, the egos come into play. Look at India, they have more senior players than Dhoni but the whole team is united under him.