comparing total group vs broken down catergory

MrNoob

According to your description, you want to make your lines ingore subgroup filtering. Right?

In your scenario, is the sub group on Legend? If so, you can create a measure and limit the filter context into entire table. 

Measure = CALCULATE(SUM(Table[Value]),ALL(Table))

Or if you need to keep the subgroup field filtering and ingore all other fields filtering, you can use ALLEXCEPT()

Measure = CALCULATE(SUM(Table[Value]),ALLEXCEPT(Table,Table[SubGroup]))

You can enable secondary axis in combo chart. 

However, currently there's no Area+Line chart in Power BI Desktop, you may try other combo chart like Column + Line chart. 

Regards,