I can see a problem if there are many September to December children deferred, who are bright and able, just with middle class parents who want to give them an advantage. That would make it more difficult for children like the one in the article. Is this the case, or is it the September to December children born prematurely or with delays who are deferred?
DS was May born where all but a few children in the class were born January to December the previous year. I can understand wanting to defer a December born child with developmental delays in that system as they would also be younger than most of the class.
If Scotland is strict on September to December deferrals then the seven month deferral cut off should be adequate. They would be in a class with other children due in the same birth month and others younger.