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?
But the C150 / 152 is not a demanding aeroplane. For a start, it doesn't demand you co-ordinate rudder and ailerons and doesn't reward you with crisp roll/turn performance if you do (it doesn't care if you do or don't!), it doesn't display classic stall characteristics (masking them with lots of washout and limited elevator authority) and it certainly doesn't demand you land it properly! (Land-o-Matic undercarriage was Cessna's claim!).
Most rewarding things in life are also demanding. The C150 / 152 is neither.