I am not sure where you got this quote from if it is a quote but are you sure the word era is correct? Could it have been "Generation" instead? Because Darken Rahl and Zedd are of 2 different generations as far as we know based on age.
and Darken Rahl's use of subtractive magic was extremely limited. Zed didn't get to be First wizard for nothing. in the book that mans ability was profound and he never exposed who much he really knew.
Also want to note that ability to wield one's Gift wasn't what made them powerful. it was the merging of the rules along with their Gift that truly made someone powerful. and Darken Rahl disregarded them to his own destruction. Not a great wizard I think.
In Wizard's First Rule, Zedd all but admitted that Rahl was more powerful. During the final Orden scene when it looked like Rahl had won, Zedd lamented to himself that he couldn't even approach Rahl's mastery with magic and that at least he had been beaten by the best.