Just a couple of points EB.
Jimmy has been around for a lot longer, so many of his appearances against Australia will have been against their prime batsmen, rather than the current crop? Whereas Broady will have been against the great pretenders?
You have listed Pakistan as the weaker minnows. This is certainly the case with the bunch that rolled up this year, but previous years they have been one of the best teams in world cricket. In Mohammad Yousuf & Younis Khan they have two of the best batsmen in world cricket during the 90s.
Surely the fair comparison is during the 3 year period that Broad has played Test Cricket, as then you can compare each of the on a level (ish) playing field, even if it is a greentop