The biggest problem with UK PPL level instruction os that mostly it is done upside down.
The most junior and least experienced instructors with the shortest service and thus more of an unknown quantity are given the responsibility for attracting new students via trial lessons and then making progress with them as well as retaining them during the hardest parts of the course - up to first solo.
New instructors should start with post solo training and the most experienced instructors should be doing the trial lessons, initial training and the final revision before test.
What other organisation promotes the apprentice to head of sales on day 1?
Too much emphasis is put on getting new instructors unrestricted rather than providing career development. CFI's / supervising instructors should be far less free with their recomendations.
Let new instructors teach post solo exercises until they have grasped the basics and then after some training be let loose to train navigation and then when they have quoite a bit of experience, start them teaching exercises 4 to 11. Finally the most experienced can teach 3 and 12/13.
The good schools will have enough of suitable good instructors who have the experience to teach all of the above and it is at that point that the school can experince the benefit of it's investment in staff training.
It is only when the instructor has demonstrated an ability to teach every aspect well that they should be recomended to have the restriction removed. If that means it takes a very long time then so be it.