Take the example in this case. EPTA were teaching a particularly difficult group of students, from a culture that is not conducive to flight training (considering the idiot who nearly gave me a heart attack with his position report the other day, I suspect they may still be). These would affect the statistics despite anything the school could do.
Other schools have students sponsored by UK airlines. They have all passed aptitude tests, so will on average fly reasonably well and be easier to teach.
As you can see, league tables would not be very much help.