The only thing standardized is the international scale to which English ability is graded. This meaning that no matter where you are from, your fluency can be measured. Employers then use this to determine a candidates suitability for a position. Much the same as they would use other qualifications to assess ability in other areas.

This is a very simple concept. One you refuse to acknowledge because it would mean agreeing with me.

Once again showing your complete ignorance about a subject, it isn't possible to fail an IELTS. IELTS is a graded exam, you sit a paper that gets progressively harder. Your paper is then marked and your ability is measured as a score from 2-9. A 2 being equivalent to A1 on the CEFR, a C1 being 7-8. So unless your student wrote absolutely nothing, it is impossible that they failed an IELTS! They could fail a CESOL, as that is an exam designed to test a certain ability, an FCE requires an aggregate score of 70% across reading, writing, listening and speaking to be awarded as a pass. But targeted exams like CESOL are given more weight by employers and universities for that very reason.

Exams like IELTS and CESOL are not scams. The fact you lack the ability to guide a student through an exam does not mean the exam is faulty. IELTS and CESOL test more than just oral fluency, so it doesn't surprise me that one of your conversation class students failed to get a decent score on an IELTS. For a good score on IELTS, candidates have to be able to read graphs and then write academically about said results. They have to read long texts of different styles and interpret the information. Spoken fluency is not enough.

I do not advocate using the same books; different classes work better with different books. There are many things to consider when choosing a course book for a class. I've never said anything about using specific course books, just another fallacy of yours.