The 1989 syllabus was not a new syllabus. As it says at the top of the 2nd page, it was only an amendment to the 1980 syllabus. There were no new topics and no topics were discarded. The only difference was that each topic was specified in a lot more detail. There was no hoo-hah regarding its release ...... in fact, many teachers in 1991 (the year it was actually used for the first time, despite what the document says) were not even aware of the existence of the new document.
And ... have you seen the 1916 paper? It is certainly not a trivial paper. I've seen my father's textbooks from Fifth Form 1951. He didn't do the highest level, and the content and difficulty looks pretty much the same as the current Ext 1 course. Fifth form was the equivalent of the current year 12 ... hence the feeling by many that they are treading water in junior school.