I never read the full series but as a child I enjoyed the ones I did read as a child. To me, the books are meant to be darkly humorous and absurdist rather than realistic so criticizing them on the grounds of not being realistic seems to miss the point of the books. It is like thinking that Monty Python and the Holy Grail is meant to be realistic. Not everything is meant to be realistic.

It is common for children’s books to feature cartoonishly evil or incompetent adults (think of books like those by Roald Dahl for example) and series often feature repeated plots and recurring villains. That is part of the appeal for many readers.