We may not use these books much but they will be good to have on your shelf if you go into theory.I am the only one from that class who went into theory. One of them I have used (Hopcroft and Ullman's White Book). The other three I never touched and no longer have. I do not know what I did with them.
He was wrong, but for an interesting reason. Two of the books were on grubby Turing Machine stuff and models. (I don't recall what the third one was.) Things like constructing a universal Turing machine with 5 states. To be fair, theory was changing: Looking at grubby Turing Machine simulations was a dying field. Hence even a complexity theorist would not be served well by these books. We didn't even do this material in that class.
However, while I can be sympathetic that the prof didn't know that complexity theory was changing, asking students to buy FOUR books that are good to have on your shelf is a terrible idea.