a Piper Warrior / Cessna 172 were like flying buses!
It's possible to turn those of mediocre skill and aptitude into qualified PPLs in a short time using them
I agree.
[It's possible to turn those of mediocre skill and aptitude into qualified PPLs in a short time using them!] .....
However, in my book that does NOT make them a good basic trainer. Probably the reverse!
Not so fast...
If a candidate learns to fly in a demanding, yet forgiving aircraft does this not provide an environment for better learning? Better learning results in a better pilot, so the objective was met? The tool did the job?
My other airplane is not at all nice in the air, and worse on the runway. It is a constant effort to keep it straight and level, and co-ordinated. A total attention demander to prevent groundlooping. I could think it is not a "good" aircraft because of this, but if you can fly it well, you can probably fly most planes well, because they are more stable, and much more nicely harmonized.
For myself, I find that when I master the less pleasant plane, the more pleasant planes come naturally. Does that not make the less pleasant plane a better trainer?