It seems to me that the Reckoners didn't actually fulfill their main goal: prove that non-Epics can and should fight Epics. Especially with the reveal that Prof is an Epic.
Two points: First, Steelheart was finally defeated by David, not the Professor. Second, the true lesson is that Epics can be redeemed, not that mortals can kill them.
Sure, in the book, the theme is explored that perhaps Epics can be redeemed. But I'm talking about within the details of the actual story. Prof specifically says that their goal is to show the normal humans that they can fight back against Epics, so that others will take up the fight. They go over this point multiple times. But, in the end, the Reckoners could not have succeeded without the aid of an Epic. David set the final trap, but he could never have lured Steelheart into that trap without Prof. Put another way, if Prof was taken out of the equation, then the Reckoners wouldn't have gotten as far as they had. It remains to be seen whether this will have any impact in the next book, i.e. whether it has to be kept secret from the populace, or if they embrace a new strategy like mutually beneficial co-existence of Epics with humans.