The key aspects of the sentence are a prospect of damage, that is itself negated by an imperviousness to criticism - so the marked as correct pair - “potent” and “strong” do not imply a criticism.
The argument advanced in the solution explanation - which states that “it can’t be damaging or injurious” because they are impervious to any damage is flawed - injurious can be defined “as likely to cause harm”. Even if we accept the definition, it’s still incorrect because the whole point of “impervious” is to negate the previous clause.
While I see what you’re getting at (and considered the same argument when answering the question myself), I ultimately agree with the solution’s explanation. On purely logical grounds, the report can’t be damaging if the party it’s meant to damage is impervious.
Even if you still disagree, it’s good to understand that these sorts of logical fallacies are used by ETS. These questions are written with the express purpose of giving us clues about what to select. A fair test maker is not going to include terms like “have little effect” and “impervious” if they wanted you to select “damaging”. Instead, you should interpret inclusions like that as tie breakers–an indicator that points away from “damaging”.