I've read and enjoyed other books by Steiner. His argument probably is that bad, but it probably isn't worse than his peers. You can spend a lifetime inn the humanities without ever seeing a really rigorous argument,

Humanities types also suffer from Typical Discipline Fallacy, assuming that everybody else's discipline is as vague as theirs, hence their affiliation with relativism, etc. For their part, STEM types go in for a fallacy of gray, treating everything less rigoroust than a mathematical proof as equally fluffy.