Well, your observation about the monarch's grandchildren has no affect whatsoever on whether their son should have been given the title of 'Prince'.
Their claim was in the past tense, not whether he would be made a prince if Prince Charles takes the throne, or anyone else.
A: Claim their son wasnt made a Prince due to racism -- lie.
B: Claim someone other than the Queen and her frailing 99 year old husband made a racist comment -- supporting 'A'.
In fact the son would NEVER have been made a Prince as they suggested in the past tense under Royal protocols.