MrsUltra the jealousy evident from some on here of your chosen course of action i.e. Supply in which you clearly do teach & mark, yet are true to your beliefs, is very interesting.
I entirely agree with your usage of the word 'spineless' to describe some of the 'S' LT you have experienced. If more staff had the courage of their convictions to point out that the Emperor actually has no clothes, the serious problems of low teacher morale and high staff turnover would have to be addressed.
Much of what has been listed by previous posters as SLT responsibility could very easily, and much more effectively, be outsourced to companies who have properly trained and qualified staff specialising in eg HRM.
Until the quality of SLT is improved so that they are deserving of respect from the staff below them, the situation will continue to deteriorate.
I would not employ an amateur gas fitter to fit a new boiler in my home, as I wouldn't want to risk my children dying of carbon monoxide poisoning. I need him to be properly trained, experienced, registered & referenced. Fortunately the government recognise this, and there is a national Code of a Practice, so I can have reasonable confidence in his CORGI registration credentials.
By the same token, I do not expect individuals untrained in key areas to be responsible for the running of my children's education. Unfortunately, I have no choice in the latter due to the current promotion system being wide open to abuse. This is fundamentally wrong.
The fact that 'S'LT spend very little, if any, time at the chalk face whilst having the power to destroy teachers' lives and students' futures is the crux of the problem.
As they ironically lecture those teachers deemed to 'need support with students' behaviour', "respect has to be earned".
I turned down AHT progression 3 x due to my zero-tolerance of hypocrisy, which is point 1 of the Person Specification.