I don't think this is true for any moral virtue. For example, the virtue of independence is not created by suffering: it is created by the need to rely on one's own judgment and actions. Along with this, there is a lot of evil and suffering that we see daily that does not teach us lessons, for example, a two-year-old child dying of cancer or a hurricane destroying homes and lives; showing compassion can be commendable. One could argue, well supported by the evidence of post-Holocaust genocides, that humanity has not taken this lesson to heart. God's purpose is to create moral individuals and he allows evil to teach us moral lessons that we are supposed to learn from. Suffering and evil are not necessary conditions for moral development. We can learn morality without being subject to evil. Likewise, deliberately exposing someone to evil in order to teach them a lesson seems outrageous. Another important problem with this theodicy is that it gives a picture of suffering. If morality depends on the existence of suffering, then if there were no suffering, then suffering would only be there to have morality or teach morality.