O’Brien believes that all literature is referential, so describing his work as derivative is a bit too easy. In fact, he defends just that in At Swim‘s epigraph,
For all things change, making way for each other. Heracles, c.416BCE.
So what if there are Joycean elements in his novel? There’s a whole lot of O’Brien there too. Joyce’s work is ingenious but admittedly peripatetic, big pee and little pee. Aristotle’s work is derivative of Plato’s, Plato’s of Socrates’ and so on and so on, but they each add something significant. It’s nigh on impossible to be entirely original, but if it’s inevitably the same shit from another mother, strive to add to the rhetoric.
Embrace your references, but not in the entitled way McEwan does, do it with flare like Shakespeare. Make your shit potent and personal. And don’t forget to say thank you.