Generate a matrix from two tables, manually populating values, preserving relationships

I'm having some trouble generating a matrix I can update, and that tracks value pairings in such a way that new or changed data doesn't corrupt the matrix relationships.

Annotation 2020-01-16 130011.png

Non-requirements:
The matrix does not need to preserve sorting or filtering on the Group or Role sheets.
The matrix does not need to 'remember' data associated with group/role pairs that have been deleted from the source sheets.

Also:
There is an ID column on the Group and Role sheets.

I'm not sure how best to achieve this. I can generate a pivot table, but I can't seem to update the values in the generated table (PT seems to be designed for data summary rather than data entry). I haven't been able to figure out how to make a query that uses the Groups table and then adds the Roles table as additional column headers, and then properly tracks manually-entered values. I have an inkling creating a data relationship might help, but unsure how to apply that.

Is there a 'best practice' or tool I should be using to achieve this? Thanks for any advice!

It wouldn't/won't let me post a link here, I don't have the required number of posts. The other site doesn't allow post editing for users with few posts, so I didn't post it there either, thought it was subsequently linked by an admin.

Thank you.