Competition improves the breed; evidently not if it impinges upon Porsche, the subsidiary lacking in innovation of late.  Porsche, as you have pointed out, was not part of the initial plan when the R8 was first developed but that shouldn’t have influenced Audi’s marketing of it, unfortunately it has since Piech has left the group.   

When the R8 was first conceived, Audi needed a follow up halo car to the TT, and this was the appropriate move.   Times have changed and SUVs dominate now, as Porsche is more, by volume, a SUV builder than sports car maker.  With the death of the R8, Audi’s racing division will basically be shut down.