group by custom column percent increase

Here is one way to do it.  It requires a series of steps: (I call your example the 'IncreaseExample' table)

Data level

1. create a table: IncreaseIDs = VALUES(IncreaseExample[ID])

    .... this is a table with just the unique IDs list, a single column

2. join IncreaseIDs to your table on the ID field

3. In this new IncreaseIDs table; create a calculated column:

     IDScore = CALCULATE((SUM(IncreaseExample[Score])))

Visuals - assuming a table visual

4. create Table visual using columns from Increase Example - undo the default and select normal dates per your example

5. create new measure

     ICalc1 = SUMX(IncreaseExample,RELATED(IncreaseIDs[idscore])-[Score])

6. create new measure

    ICalc2 = SUMX(IncreaseExample,[Score]-[ICalc1])

7. create new measure

    IPct = SUMX(IncreaseExample,
                            IF([ICalc2]>0,[ICalc2]/[ICalc1],0))

IPct measure is the final - you will want to option that to display as a Percentage

ICalc1 and ICalc2 do not need to display in the final visual