The fact that Harris said that bombing alone could do it was sheer hyperbole. Did he really believe that? I've no idea, but anyway what difference did it make other than to ensure that you had an utterly determined man at the helm?
If Admiral Cunningham (ABC, viewed by some as the greatest Allied commander in the 2nd World War) is to be believed, he did. ABC recorded in his diary after the final conference and presentation to the King, Churchill and all the Chiefs of Staff of the OVERLORD Plan (D-Day landings), on May 15th 1944: "Bomber Harris explained what a nuisance this Overlord operation was, and how it interfered with the right way to defeat the Germans, i.e. by bombing." [See
Cunningham - the greatest admiral since Nelson, by John Winton]
"Colonial warmonger"? dunno. Pig headed and stupid? looks like it. And his persistent denial to Coastal Command of the resources it needed contributed to huge loss of life and materiel in the Battle of the Atlantic. Not a hero.