As far as the CFI milking you for hours.
I had that impression when I did my Single Engine Commecial in Usa. The CFI merely said "thats not good enough..now do it again"
without pointing out my errors. I knew I were taken for a ride, but since I were almost done I just rode it out and got my lisence. It didnt cost me that much more, but it were a frustrating feeling.
And keeping someone for 50 hours before solo..well..depends on how frequent you fly.
If you fly once a month etc you lose alot of the touch and need to be retrained on what your last lesson were about. But..still 50 hours sounds like milking to me.
But looking at Part 61 in FAR (USA) there are are a certain manuvers you have to be proficient in and there is NO WAY it can be done in 4-6 hours. And by not getting your student proficient, your actually breaking the law.
As far as the student growing on the solo expirience. Sure..I remember when I soloed myself. I felt great achivement and my will to push myself harder increased. Ive seen the same on my students also. They improve alot after going solo.
But...if you havent trained your student sufficient, he/she might not get thru the solo expirience 100%. What if he/she faces a situation that werent presented earlier and he/she has no knowledge/skills to recover from that situation? Sometimes this will scare a student so much that the joy of flying is gone..or in worst case, the student dies.
Solo makes the student grow, but only if he/she survive.
I know this is a very cynical and grim way of expressing my thoughts, but Im just trying to prove a point. It might be extreme and a one in 10000, but when it happens, both you and the student wished that you had gone deeper into the training.