I don't think Terry Nation was a hack, I suspect he just didn't really have much passion for DW, or the Daleks. The BBC would buy just about anything he wrote about the Daleks, so he got lazy and would just crank out any old thing for a paycheck.
It wasn't until (if true), the script editors called him on it during the 4th Doctors era ("It's a terrific story Terry, but you've already sold it to us six times.") that he buckled down and put some effort into producing Genesis.
According to the special feature on the Destiny of the Daleks, it was Barry Letts who said that, but it was three times. Letts also suggested the concept and title of Genesis of the Daleks.
Mr Awe