As a teacher I will try to address the questions you've asked:
Sometimes I use my professional judgement and ask the TA to work with another group of children who are action or action + who have no TA support. I will always ensure that the statemented child is supported and has appropriate work. In the right circumstances, I believe that the child with the statement needs some breathing space from constant adult support and it's useful for them to try to work independently. There are some children however I would never leave alone. It depends on the child.
I don't know what you mean by 'believe' in sublevels. I teach a SATs year group and I know that they exist and know them inside out. I can give a sublevel for any child in my core subject classes.
I never make APP judgements up. It takes hours of time collating and evidencing for each child in the class. If done properly it cannot be made up. If you think they are making up judgements ask to see the evidence to support their claims. They should at least have marked a piece of work in a book as evidence of a level or should have a folder of evidence.