Danny, the piece I quoted from was mainly about the aircraft rather than the training syllabus. It was a single unnamed ex-student's recollection anyway, so hardly the final word I'd suggest. What the article does mention is the preference for the Stearman by many instructors as a basic trainer, rather than the more "slippery" Ryan and Fairchild monoplanes that many students preferred as being closer in design to the fighters that they hoped eventually to fly. So is it possible that the "seat of the pants" philosophy was coming from the civilian instructors who had flown bi-planes throughout their careers rather than an official USAAC requirement?
If the quote is only half right it would seem that being denied only the ASI meant that you got off relatively lightly, yet gained valuable insight into extracting a desired IAS from your attitude and an appropriate power setting as well as the ability to suspect the ASI if it didn't correlate accordingly. High performance WWII operational aircraft would not be very forgiving of such a routine, or perhaps even the advanced trainers. If the custom lingered on I doubt it outlasted the Stearmans, though they did continue on into the early post war years:-
The PT-19 has been wrongly described as
being THE primary trainer of WWII. It was the Stearman,
which also saw service during the early Cold War years and
helped to train some of the country’s future astronauts
None of which gives a definitive answer to your question. I'll keep up the search, and I invite others to do likewise.
