Quigley wasn't his astrologer at the time. I believe she was either dismissed from his service, or had left for some other reason. She was called back to his service after the shooting.
"Today, people’s blind belief in the power of astrology to reveal the future strikes us as absurd, because our mental stance is radically different."
Blind belief in anything is absurd.
This guy seems to conflate pop astrologers / grifters with actual astrologers. The grifters will claim to be able to predict the future. Actual astrologers will claim to explain the fields of possibility that will present themselves to people using archetypal languages; this is what astrology 'actually is': a language of archetypes. It has been my experience that 100% of the time it is people who know very little about astrology (like the author of this article) who deride it as 'false'. But that's about as useful as saying chemistry or Swahili is false.
"the astrologer-physician predicted that Hamilton would live happily, but would be in danger of dying from cardiac disease", "he predicted a life of political as well as ecclesiastical power.", "he foretold that the young king was going to live a long life"
This... is not how astrology works at all. Grifter or just woefully uninformed.
We don't go around proclaiming that physics is trash because of Newton.