You call it "cruel" to point out the simple truth that the cover was inappropriate and ill-suited to the text of the comic? That is solidarity. It's because I am a creator that I have no tolerance for bad art. If I were a civil engineer, and I saw someone design a crappy bridge, should I really pretend it's a good one? If I were a chef, and I saw someone undercooking a fish plate, should I really pretend that it's properly done? If I were a priest, and I heard another minister preaching a totally ass-backwards interpretation of the Gospel, should I really just nod and smile? If I were a janitor, and I saw someone cleaning a building inefficiently and with totally the wrong kind of soap, should I really pretend he's awesome at his job?
No. I should correct them, because if I take my job seriously, if I really believe it's important, then I want to see it done right. And I'm doing a disservice to both the person who's doing it wrong and the people being served by that person to let them continue to be less than the best - whether it's lives, souls, food poisoning or just clean tiles on the line.