I really wish this comparison would go away. SAF was a builder who rebuilt clubs from the ground up, including a focus on taking up and coming players cheap or youngsters though the academy and making them the best they could be. That's what he did at Aberdeen and what he was doing at United, as could be seen in the excellent players he was picking up in the late 80s, the improvements in the scouting and the change in the drinking culture. That, by its very nature, takes time.
(also, who are these "many expensive signings that didn't work out?")
Mourinho is a short term results manager, who has never once undertaken a long term rebuilding job in his life, or even shown the inclination to do so. He buys for the now and he handles his players for the now, with no pretence of a long term vision . Indeed, we hired him because he is a short term manager, and we wanted a short term result. It didn't work out, such is life, but pretending he's something he's not is simply folly and comparing the two is pointless.