I doubt whether a distinction can be made between lens sharpness (or lack thereof) and diffraction.
From DPL and lens diffraction - #5 by Benoit
This said, when diffraction is strong (or more generally when input lens sharpness is very poor), our dxo modules limit their correction by default, as fully correcting the picture might lead to artifacts (and when a small detail is very blurry, there’s not that much to do to recover it…). Nonetheless, adjusting manually lens sharpness sliders enables to increase again sharpness.
George