I gather that USAF Slingsby mishaps were engine related (or pilot induced, or a bit of both), rather than a result of spin characteristics. Hasn't stopped the RAF from continuing with them through their civvie contractors. Odd to compare a Bulldog to an AA 5 (can an AA 5 aerobat, or land in a 25 knot crosswind?). Anyway, RAF Bulldogs had some odd spinning incidents but weren't binned as a result. I've spun a Bulldog and wouldn't necessarily describe it as docile.
Mr Moto's description of the perfect trainer fits something like an, er.... Tiger Moth. David Robson, in the preface to his recent (very good) book on aerobatics, says this:-
"Aircraft such as the Tiger Moth, Chipmunk and the Stearman were effective trainers because they developed good hand/eye coodination, an awareness of and a respect for airspeed, a discipline for flightpath control and a sensitivity to surface winds. They were a challenge to fly accurately and well. They taught correct habit patterns and responses - essential to the automatic correction of flightpath or airspeed deviations. The touring aircraft that currently populate the majority of the world's training fleets are not suitable trainers for other than cross-country and procedural training".
I don't know enough about different types, or flying generally, to judge whether he's right, but his view seems to be a respectable counter argument to the "better learn in a spamcan" idea. Anyway, they're all aeroplanes and therefore by definition wonderful.