Streaky or not, his goal and assist returns always finish up streets ahead of most of his peers. He's scored 12 and assisted 12 so far during what is considered to be a "bad season" for him, with a lengthy early injury layoff to factor in. And scoring/directly creating is only half of his role for the team- he also contributes universes more than Defoe to the team as a whole both in building attacks, tracking back and even man-marking opposition attackers if needs be. They're not even comparable players- Rooney is a whole different, more complete type of player with a dozens more attributes, except he also adds JD's goal figures on top as well.
The fitness thing is a real concern, though, and add that to his wages and the fact I mentioned earlier that he can be awkward to slot into a pre-fixed system and he gets a do no want from me.