“r.Crusoe” is treif, but the sin of lashon hara can be likened to murder, so it is very important to say not to say lashon hara-the Rabbi thought the book was a biography “co-written” with Defoe, and as I explained previosly above – it is clear he did not read it.
To say what you said about a gadol IS derogatory, and IS lason hara.
The definition of lashon hara extends to things that may be true also. However you have to use your sechel also, to see that a book on a shelf ( of which the person may not even be fully aware ) does not prove he read it.
That several people with slightly circumscribed writing and spelling skills may say to the contrary, will never convince anyone that suitable Jewish books are in any way lacking for the purposes of teaching English – they are not.