I'm not sure what else the guy can be doing to be honest. He's not getting the chances so is frustrated, which was evident when he went and booted the hoardings after the miss v United. His first-touch and passing is top-notch though, he's created a lot for us even if he's not scoring too many (yadda yadda yadda strikers are judged on goals blah blah blah).
Whenever we bring Defoe on in games we just don't look threatening any more, he was awful against United in his 20 minutes. Think the difference in styles between Defoe & Ade and Soldado is that Soldado tends to stay central on the shoulder of the last man, Defoe and Ade both drift out to the wings so although they get more involved they're never where they need to be when it comes into the box.
Tough call but i'd stick with Soldado for now.