Is it discrimination under Equality Act 2010? and is this considered a safeguarding issue?

Son is a full time wheelchair user (unable to stand or crawl) year 3 at mainstream village school. There were adaptions needed to access the top playground (keystage 2) and a ramp was put in last year.
On the 17th May, he suddenly said children were allowed to play on the grass bank alongside the playground (this is quite steep and the kids often roll down it). My son described how he felt sad and lonely as all he could do was sit and watch his friends. We explained this to the headteacher who at first defensively said:
1) No children are allowed on the bank, shortly after 2) The children are only allowed on the bank when i'm there 3) Then 10 minutes later, advised there were no rules about the bank. When further talks were had she advised she cant stop the kids going on as its the 'shaded area'.
My son told her how he felt and she said to him whilst I was sitting there "Its really fun going on the bank, that's why the children want to go on there, but they'll move onto something again soon."
We had asked if there could be rules applied that limited 2 houses (school are divided into 4 houses) on the bank at any one time. This would ensure that our son had some friends down on the playground with him at all times. No further communication from the head. We had also questioned why our sons 1-1 had not seen him alone and offered support, but this was not addressed.
On the 5th July, our son was upset again as he was made to feel this way again. When we questioned why this had not been addressed or rules put in place, we were told the Senco was meeting with the School Council (made up of children aged 8-10 years) the following week to decide the rules.
The rules they came back with is that each classroom/year group of 30 children are allowcated 2 x 30 minutes sessions at lunch on certain days.
We said that this per class (only one class per year at school) will make our son feel even more isolated from his peers.
We raised a complaint and have been told its not under the Equality Act 2010 as its a physical feature - but we are not asking them to flatten it, but just make reasonable adjustment to their rules/policies.
Also stated its not a safe guarding issue - surely if it is having an effect on our sons Mental Health and using the words that the head said to him, it is safeguarding.
We lodged a complaint to the governors whom have sent a really weak reply saying "the head never intended to cause any offence and regrets the vocabulary chosen.
They have looked at the timetables and confident our son receives 1-1 dedicated support. (That's as per his EHCP).
There has been a few things happen previously like everytime our son moves areas, new equipment has been put in the playgrounds from reception and key stage 1. Then when he moved up to this one, they got an accessible grant and the Head wanted to put in 'monkey bars' using the money, my son told us and we were able to speak with school and find something more appropriate but there seems little thought.
Just wanting for the head to take responsibility and show some care.
Any advice would be gratefully received.
Thank you.