I believe Daz probably did ghostwrite some of those beats. The best beats from day 1 have been sampled though. Dre just did it the best at that time, regardless of tactics. He still had hits without sampling after that.
The first "successful" rap song ever was "Rapper's Delight" which sampled a semi-popular disco track. At least 50% of the best tracks of all time are sample-based, so I will never knock it