I agree, you need to take into account the entire situation regarding staggered starts / half days, and the potential chaos it creates for the child/ren.
In theory a gradual start to school sounds great, as it provides a chance for children to explore their classroom and experience the school day without being overwhelmed. Smaller groups also sounds lovely as it allows the teacher / staff to get to know their new pupils and spend more 1-1 time with them, without the worry of assisting 29 other children
However that's not the entire story.
Staggered starts also means
Children doing random half days, missing days, and being in a routine that isn't realistic or reflective of a normal school day.
Some children being collected by mum, then dad, then a day at home, then a day in nursery, or with a different person each day.
Some children start school only to then find themselves back at nursery, whcih can be confusing, especially as nurseries do quite a lot of transition work with a focus on being school ready.
Some parents take annual leave which means the child spends more time at home with a parent. They then get used to this routine for a few weeks, only to then have to learn to adapt to another routine when the half days / staggered starts finally ends, and this can make the transistion to school, and being away from that parent quite difficult.
Some parents who take annual leave for the start are then unable to take time off in the holidays. Meaning young children having to attend holiday care (often with much older children) or have a random ad-hoc arrangement with multiple carers
Children spending time with a small group of children and enjoying the nurturing 1-1 attention, only to then become overwhelmed by a noisy and busy classroom.