I don't accept that staff are "labelled" 'senior' teachers - they have applied for a particular role and have been appointed to fulfil it. The additional responsibilities which come with that role mean that they would not be able to do a full teaching load in addition. Were you expected to do the subject leader role with not even one additional hour per week?
These Jeremy Kyle style conversations (and I agree with that term - some are beyond ridiculous) are not solely held by senior teachers. But teachers have a right (in my opinion) to pass on difficult conversations to senior teachers, and be supported by them. I don't think it's acceptable for teachers to have to ring Mr or Mrs Difficult Parent about sexual misconduct or theft or serious bullying. It is in some ways a waste of time (although if you are experienced enough you can often get parents on side) but it is a necessity. Those conversations need to be had, unfortunately. And in some schools very regularly. I would also say that some roles can make a vast difference to the experience of teachers. For example, a strong head of year or SLT member whose discipline is excellent, can have very far reaching influence. They can go into lessons and get the kids behaving properly so that they learn. The impact that they have is often far greater across many classes or year groups than in teaching one class themselves. If they have that time to go round lessons it can be extremely effective.
The burden of teaching time that teachers have is unfair in comparison with other countries, I agree with that, but not an unfair burden in comparison with main scale teachers across the country in state schools. I think it is very fair that heads of year, department leaders, SLT and headteachers have less teaching time because they have a hell of a lot of other responsibilities which they would not be able to fulfil if they had no time, and that would then have to revert to main scale teachers, which would be unfair.
When I was a new teacher, I would have felt pretty worried if I was told that there was nobody to lead my department or year group or school or to plan the assessments and schemes of learning and no support network available to help or advise with difficult classes or parents. I would have felt pretty alone.
Conversely, I can think of a lot of senior leaders who would be thrilled to bits to be told that they could have a couple of extra classes in return for not having to manage any difficult staffing situations or tricky parents or marauding kids. But they accept that is their role and they are paid more to deal with really shitty and delicate situations, and they are allocated some time during the school day to do it.