If you withdraw your child from school to HE them, then you need to inform the local authority, otherwise your child is legally truant.
You have this wrong. You have to inform the school that you are withdrawing your child to home educate. The school is the one with a duty to then inform the local authority, not the parents. Many schools are terrible at doing this and that's where the blame should be put.
We withdrew both our DDs at different times from different schools. The primary school informed the local authority, the secondary, a year later, didn't. The fact that DD1 was being home educated came to light when she was in professional panto and had to have a performance licence, then they panicked. That was a failure of the school, not us. We informed who we were meant to. Parents aren't meant to have to go all up the chain trying to find the right department.
We were inspected once a year. After the first year or two it became rather pointless, even by the inspector's admission. They were never able to offer any help, support or advice, even though it was meant to be a two way street. Every year the man who came round said "your girls are very lucky. I wish I'd had an education this good". It was obvious to all we were educating well, year after year. They could see we were responsible parents with our children's best interests at heart and that wasn't going to change. It was merely a box ticking exercise, diverting resources away from those who may have genuinely needed it.
In the main I do agree with you, OP, that local authorities should at least know who the home educated children are and check that they are being provided with a suitable education. I think the reason home educators are opposing the government measures is because it's the thin end of the wedge to all sorts of other things, such as having to mirror schools, and having to allow a stranger you've never met inside your house to talk to your child, possibly without you (this was mooted some while back). This doesn't happen to any other families unless concerns have been raised to SS, and home educating by itself is not a cause for concern (even the authorities agree on this). On this point we should all be wary, because what's next? Inspection in the summer holidays and before children start school? Authorities being allowed access to our homes for a myriad other reasons? Rights are eroded very slowly, bit by bit, until we turn round, realising our every move is accounted for, inspected, recorded, and wonder how it happened.