You first mentioned that they were "hanging their hats on 30 year old cases", which would place the victims, assuming they were 5-15 at the time of the crime, in the lower 40s age range max.
So, even by your assumptions, we are not talking about 60 year olds here.
As mentioned previously, children of JW parents are likely not going to go to RV. Therefore, the pool of victims likely to speak up will mostly be adults, and out of that pool only those with enough courage to speak up against the holy org. So the apologist excuse that the typical victim is an adult and likely exJW is neither surprising nor a valid argument against the systemic issues plaguing the religion's handling of child abuse within it's ranks.
Over the years, Watchtower has reacted to the backlash and somewhat revised some of it's policies for the better (two witnesses can be of different events, don't force victim to personally confront abuser), but as the ARC found, there are still troubling problems. More investigation is needed indeed.