Hi there,
Although most schools stop practicing this as extra 6 months to a year more of untrained contract stint could delay your promotion in the later years when you start your actual teaching stint. However, at your end, it is likely not possible to change this practice at your school if your school leaders believe in this practice. Let's have a growth mindset, I would say that take this chance to experience a full year in school to see if you are able to handle the responsibilities as a teacher while clocking experiences that would helpful when you become a actual teacher. In the some cases, I do know of people who quit after the six month stint as they realized that teaching in main stream school is not for them.