Thinking of this as giving him an advantage compared to his peers is kind of a waste of time, a moot point. You’ll never know the answer there, there will always be brighter and poorer children than your own. If you think a year would benefit your child - a year more play, a year to grow more mature, a year to gain more confidence in the world - then go for it.
I’m in Scotland, I sent my Nov born DC1 to school at 4y9m and then Feb born DC2 at 5y6m. DC1 was more confident and social when she started, but she just wasn’t ready for the restrictions of P1. She didn’t try at her work and really didn’t care if the teacher thought she’d done a good job or not. She just wanted to play (because she was 4!). DC2 is generally more nervous and shy but when he started P1 he flew. It was such a relief, he was ready to learn and grasped things quickly and loved it.
The rules have just changed in Scotland and now I can defer my Oct born DC3. Academically and socially she is totally ready for P1, but she is so similar to her big sister. She doesn’t want to sit for long and do jobs, she wants to play, which is completely appropriate, because she is 4. Another year in nursery will be enjoyable for her I think, but if she gets bored, that’s fine, children need to learn to deal with boredom.
There is also something to be said for this age group of children and the effects of Covid. They missed so much. They don’t remember it now and don’t know any different, but I think they deserve more time before the demands of school kick in because they lost out on many normal baby and toddler experiences. Not to mention the fact that speech and language difficulties among these children have sky rocketed - this has an impact on teaching time for all the children in the class. If your child is super ready then the impact of lack of support will be lessened.