IMHO you can't really compare a regular middle order batsman to someone who most of the times comes in the 45th over and has to slog it out. The former gets ample time to get his eye in and build an innings, the later doesn't have that luxury (and Jadeja is not a natural slogger).
Since this is a comparison thread, allow me to post a few stats about their domestic careers so far, which might (or might not) give a fair idea about the topic in hand.
Shakib (Batting, FC career)
Mat Inns NO Runs HS Ave 100 50
65 120 9 3886 144 35 5 23
Jadeja (Batting, FC career)
Mat Inns NO Runs HS Ave 100 50
48 70 6 3263 331 50.98 7 12
Both the players have different roles to play in their team. One has been doing it brilliantly for a few years now, and the other has started doing in recently. Both Shakib (for sure) and Jadeja (I hope) has a long career ahead of them, so lets just leave it to that. And regarding ICC rankings, wasn't at one point Ireland was ranked higher than Australia in T20s?
