I was instructing on Vampires when the changeover from Piston Provost to JP3 was happening.We noticed an immediate drop in skills. When we went to fly the JP we realised why, it was too easy to fly. Basic trainers need to be sufficiently challenging to identify those with inadequate skills, or they just fail more expensively further up the line.
i met the same problem when instructing-on helicopters on the change over from Sioux/Whirlwind to all through Whirlwind, particularly when the requirement to do all exercises with manual throttle was eliminated. Nobody failed! They just failed at the OCU stage on Wessex or Puma.
I think that was what made the Tiger Moth a good trainer. It was (and is) not the easiest aircraft to fly well. I’ve flown those as well. It’s successor the Chipmunk was an excellent grading trainer for sorting out the wheat from the chaff.