Users assigned to Child org unit can not delete the profiles assigned to parent unit in the UI delete option. This is working as expected. However, same Users assigned to Child org unit can DELETE the profiles assigned to parent unit by running the Workflow. Is this a product bug?
It doesn't look like it has been reported as a bug, so I'd suggest submitting a ticket to Campaign Support if you want to get it changed. It will need to be reviewed by Adobe's R&D team to determine if it's a bug or would be considered an enhancement.