God’s justice doesn’t really pertain to what happens to us in this life, it’s about the eternal reward / consequence of our choices.
I can chose to do evil, which causes human injustice against others. God’s justice is not served by putting an end to that evil in life, that is human justice. God’s justice is in the eternal suffering I will experience as a result of my rejection of Him. Similarly, for those innocent people whom I harm, if they are truly innocent, then His justice will be in the eternal reward they receive.
The problem with your position is that you are only considering this life, and in this life we are not guaranteed anything. It is not unjust for God to allow someone to die, because God does not owe that person a certain length of life. It is not unjust for God to allow an individual to suffer because God does not owe us a life without suffering. In fact, it may be God’s desire for mercy which allows a person or group to suffer. I know that many people do not turn to Him until they have nowhere else to turn. While it is regrettable that that is what it took, the benefit of turning to God in those times of suffering far outweighs the magnitude of the suffering itself, especially in light of the eternal ramifications of that choice.
Consider in the OT when God allowed the Israelites to suffer. In every case, their suffering was the direct result of a collective rejection of God. it’s true that many people suffered, and that God could have intervened, but through their suffering the people repented and turned back to Him. That is, by far, the greater concern, and the greatest concern of our lives. Eternal salvation is worth the suffering, especially if that’s what it takes to get someone to turn to Him and accept the gift of salvation.
We have, as a species, adopted this faulty notion that somehow we are owed a certain kind of life. When we do not get that kind of life we believe God is being unjust. In reality, everything that we have is a gift. Our very lives are a gift freely given, one that we could not earn, and one that we do not deserve. How much more so the salvation, freely given, and paid for through the blood of the cross? In that, we see the depths to which God is willing to go to impart these gifts. It was the greatest possible injustice that God be killed for the sins of His creation, yet He embraced it freely out of love for us, and through that infinite injustice, He brought salvation into the world.