The people who do this are invested in a fantasy they want to be reality.
In any fair appraisal of the schools, you have to consider the actual alternative, not some fantasy put forward a hundred years after the fact.
The schools were an improvement over what went on in the villages.
The residential schools were a government mandated and funded program.
Religious organizations were contracted to run the schools under government rules.
The graves issue is a product of the underfunding of the program.
There was not enough money to feed the children or adequately heat the buildings. Therefore the children were weak and subject to disease.
Also there was no money to send the bodies of children home if they died. Nor was there any money for stone grave markers and so the grave markers simple wood markers that quickly decayed.
As for records of grave yards; creating and keeping records of graves cost money as does maintaining those records.
It should not be a surprise that these records do not exist.
This will devolve into a move for reparations.