Here you can compare with my solution, it will give you the percent of the parent.
with
member [Measures].[Percent of parent] as
([Measures].[Order Quantity]) /
([Product].[Product Categories].currentmember.parent,
[Measures].[Order Quantity])
,format_string = "percent"
SELECT
{([Measures].[Order Quantity]),
([Measures].[Percent of parent])} ON COLUMNS,
{[Product].[Product Categories].[Category].&[3]} *
{[Product].[Subcategory].[Subcategory].Members} *
{[Product].[Style].[Style].Members} *
{[Product].[Product].members}
ON ROWS
FROM [Cube]
I don´t know if i read your dimensions correctly but maybe your member should look something like:
with member [Measures].[Percent] as
[Measures].[AGG_RATING Count] /
([DIM RATING STRINGS].[LABEL].CURRENTMEMBER.PARENT,
[Measures].[AGG_RATING Count])
, format_string = "percent"