Derrida’s Speech of Philosophy, despite being devoted exclusively to Husserl and a close reading of certain key moments in Husserl’s thought is not a work of scholarship but a genuine work of philosophy in its own right. Derrida does not set out to represent Husserl, but produces something new in and through Husserl.
Heidegger’s Sophist lectures or his massive four volumes on Nietzsche, while engaging with a particular thinker, are not scholarship but genuine works of philosophy.
Iain Hamilton Grant’s book on Schelling is not scholarship, though it is very scholarly, but is a genuine work of philosophy. Although the dividing line is fuzzy, the difference between a scholarly work on a philosopher and a philosophical engagement with a philosopher seems to revolve around whether the work seeks to represent the philosopher or whether it is engaging with the philosopher to produce a new work of philosophy.
In this respect, my Difference and Givenness is a work of scholarship insofar as it seeks to represent Deleuze and explain his transcendental empiricism and how it is working with the rationalist tradition and the tradition of transcendental idealism,
whereas DeLanda’s Intensive Science and Virtual Philosophy is a genuine work of philosophy in that it takes up Deleuze’s thought to produce a philosophical work of its own. Both types of work are valuable and make their own contributions.