Not at all. I wouldn't say it was my favorite book if I couldn't answer that. But what was the Grand Inquisitor about? Who tells that story? It's Ivan. The cynic, the rationalist, the atheist. First and formost the Grand Inquisitor is about the views of Ivan- and the modern world- towards Alyosha- the man of faith. Ivan picks that story to demonstrate how he- and the people he represents- see all of the faithful. Like his Brother Alyosha, hence not only catholics, but the Orthodox, or any other believers. But Dostoevsky also throughs down a challenge to Christians in that story about our free will and human nature. And we could go on discussing the meaning of the Grand Inquisitor indefinitely- and I hope we will.
But I think Christians for the most part identify with Alyosha, so that we all have to answer Ivan's Grand Inquisitor. Because that is the modern world trying to counter our beliefs. It's Ivan's way of talking to his Brother about his atheism- and his doubts about atheism- and the incurable love of humanity as he puts it.