Does the thought that this worldly life is unfair, and that a person may not attain in it the happiness and comfort they deserve, contradict religion, despite the belief that God is The Just and that what He decrees is good?

This world is a realm of trial and tribulation, not a realm of recompense and permanence. Allah did not create it except to test His servants. It is a fleeting enjoyment compared to the Hereafter, so its justice should not be judged in isolation from the Hereafter. This world may be a prison for the believer and a paradise for the disbeliever, and it holds no value in the sight of Allah. Therefore, it is no wonder that trials are intensified for prophets and righteous people in it, and that Allah’s enemies are granted abundance. If the questioner means that this world is not a criterion for distinguishing between people, and that acquiring its splendor does not indicate Allah’s pleasure, then this is correct, just as absolute justice will only be in the Hereafter. More important than all of this is asceticism in this world and working for the Hereafter.