I suspect the "chop" rate in pilot training has always been higher than for other aircrew specialisms, if only because the physical skills required are difficult to assess until they are actually put to the test, but I cant believe 90% or anything like it.
On my own nav course of 12 in 1969-70 we had two chopped pilots, as did most courses at that time. These usually went on to qualify as navs, and in fact our actual failure rate, leaving aside the odd re-course) was quite low, probably around 10-15% at the most overall.
As an aside I was never offered pilot training after my initial assessment which in the event was a good decision, as although I subsequently learned to fly to PPL level, I took so flipping long to go solo I'd have been out on my ear at a much earlier stage had this been at an FTS!