People can easily overcome their fallen nature by having faith in God, praying to God, accepting Jesus Christ completely, following Jesus Christ's teachings, following God's commandments as best as they could, doing their best to avoid sins, and repenting of sins whenever possible. Of course, easily in the sense that there is a complete formula for how to do it, but not easily in effort obviously as that involves a lot of hard work and requires a lot of suffering along the way. In any case, eventually people who do all of that sufficiently enough are freed completely from the grasp of the Devil and stop questioning God like you're doing. This questioning is often invited by Satan to people who have gaps in their faith and behavior due to intentionally sinning without repentance or having unrepented sins they are too proud/stubborn to admit and repent of. Once you overcome such petty holdbacks, you realize that it is a gift to be alive in the first place and that without obedience to God, people would be more devoid of morals than anything you described as they'd be living a "dog eat dog" proud greedy blindly-lustful mentality instead of Christian turn-the-other-cheek meekness and kindness. As such, always pray to God to be protected by the Holy Spirit from such questioning thoughts. They come from the Devil and must be given no attention or importance whatsoever. After all, God created you and gave you the very brain and morals you are using to entertain such thoughts. Otherwise, you would have been no different from a dog skinning other animals alive without remorse. Also, who are you to question God anyways? Obviously no one worthy of questioning the Lord, the creator of heaven, earth, and all living things. Besides, since God is above all human judgement, he could do whatever he wants, and anything he does is good since it comes from him, the creator, and wouldn't have existed in the first place otherwise. After all, even if God happens to have created an earth where everyone freely chose evil over good except for one person, then what God did is still good for the one person who chose good over evil even if the rest will all sadly perish in Hell as a result of their inequity, disobedience, and irresponsibility. God did give them enough power to choose good over evil, but they disregarded his gifts, commandments, and warnings (remember there is always enough window for someone to escape temptation, but they have to take the right action right away, not commit the sin of sloth). Is God cruel for his judgement of man? Of course not! Who am I to judge God? Let alone I'd be intentionally committing the sin of pride and error of irrational thinking if I did judge him given I am nobody compared to him as a created human being whose brain came from God in the first place. Is God more fierce than North Korea's president!? Dahhh!! God is obviously stronger than everybody on earth, including President Trump, Putin, and Netanyahu, to name a few country leaders, and could hurt evil folks more than anyone on earth. Does that mean God is evil? This goes back to me not being in a position to judge God. Still, scripture says God is good, and I am called to believe and repeat that and only that out of obedience to God to go to Heaven, so that is the truth I accept. In any case, if I were to think of it logically, punishment of evil is good, so God is obviously good for punishing evildoers mercilessly after they've been given enough chances and then neglecting to do what's right. Do I feel comfortable with God being that way? I do after having cleansed my soul from evil, but I most certainly did not feel that way when I was in the grip of Satan before I was born again. It took a process of regeneration through the Holy Spirit by keeping God's commandments as best as I could for a while before I started getting comfortable with God, no matter his brutality. Of course, the biggest takeaway is that if you don't believe in God and obey him for petty nonsensical reasons such as "Oh, God is too cruel! I don't want to follow a cruel God!", God is still present with you believing in him or without you, and will exercise his fierce judgement upon you and put you in Hell on Judgement Day as a result. God can do whatever he wants, period.
Godspeed.