It was fairly gutsy of them to do this at the time, considering the COS was very, very good at crushing their critics back then. But then, who the hell read these comics? Just teenagers like me at the time, who were therefore inoculated against the Church when it appeared. I lived in the South, so I would never have heard of them then otherwise.
Pasko, on the other hand, lived in LA, and only someone in that city could have written this with such familiarity.
As far as how dead-on it is: one thing I find fascinating about some of the words L. Ron Hubbard made up is how they seem designed to test credulity, like you can detect in them a joke on those he's fooling. One example? A planet of one of those ancient races "Xenu" enslaved is called "Arslycus." I know how they prefer it pronounced, but somehow I found a different way more plausible.