The question will still rise as to the quality of Pacquiao's opponents during his 2-year IBF Super bantamweight and 10-month WBC Flyweight title reigns. Though Pacquiao did had some very impressive and memorable fights against Barrera, Morales, and Marquez, most of which are money fights. What made great fighters go down in history are title fights, and the quality of their opponents in such fights.
Today's rankings will soon wither in time, but the belt and the record will always be there to prove who Manny Pacquiao really is and what kind of opponents he did defeat. And Manny Pacquiao became well known as a Super featherweight fighter and most of his better opponents in his career are from the same division, he should prove that he's the best by winning the Super featherweight belt.
Barrera and Morales are already out, what's left for him is Juan Miguel Marquez. Joan Guzman and Edwin Valero can wait for their turn.