Well, that feels like trashing eleven years of my career, plus the post graduate additional qualifications I got!
All SENCos new in post must do the qualification if they haven't been a SENCo previously. That will consist of attendance at a university course, projects and dissertations. The Code of Practice for SEND, changed in September 2014, removing and amalgamating categories in schools and changing from statements of SEN to EHCPs. These have to be completed by 2018 (I think.)
The responsibility for teaching children with SEND lies with the subject or class teacher. All teachers are teachers of all children. OP, you are looking at the job from your own perspective. You are not and cannot be aware of all the constraints on the time and resources of schools. SENCOs are often juggling the needs of the children for whom they co-ordinate provision, with the requirements of their teaching load, the instructions from the SLT and the needs of Ofsted.
I ran a department with 20 staff, a specialist centre for S&L and 40 pupils with statements. I also taught (at various times) core skills, RE, ASDAN, Circle time, PSHE, as well as all the meetings, social care, LAC etc, etc, etc.
It might not be what you think is right OP, but please look at it from a different viewpoint and look at how you can work collaboratively with schools, rather than focus on what they're doing that is wrong.