Don’t get too caught up in the hothousing for SATs idea.
A lot more things happen in Y6 than SATs.
Being in the oldest cohort in the school often leads to little privileges and responsibilities which help with confidence building, self esteem etc
Some schools do a Y6 school journey which can be great for encouraging independence, give opportunities to try out new activities,
Leavers events, parties, saying goodbye to staff classmates and friends can be a rite of passage.
Friendships often develop as children get more independent, eg walking to school together without no adult.
It is a year when children do mature, some are coming into puberty, some have more independence, they are very aware that in Y7 they will be starting at the bottom of the ladder and many enjoy their year as top dogs!
Don't underestimate the soft curriculum that children get in school, eg learning about working alongside others, listening to others, understanding that other people have different opinions, skills, opportunities.
If you really think your child won’t cope with Y6 because of SATS ( and to be honest it sounds as though it is your idea , not his) then by all means remove him and home school, but I would discuss it with him first and consider together what emotionally positive and fun aspects of school he would be missing out on. You won’t be able to remove him from all tests, exams, stressful situations in his school career so maybe giving him the idea that these are optional is not necessarily a good move.