He presupposes that the souls inherent nature determines their quality of life. I don't know anything about Hinduism, but I've heard that when it comes to reincarnation at least in some other religions, the quality of life is dependent on the souls behavior in a previous life. So if you're an evil soul, you do evil things in a life, and then you experience evil things in life. It could be that neutral souls do neutral deeds, and are reincarnated into more neutral lives. If God didn't create those souls, he is simply placing them in the life that they deserve based on the souls inherent nature.
My problem with religion isn't that the beliefs aren't plausible, they are if you do enough mental gymnastics. The problem is that religions are based off of lack of evidence. Most of them work because they are unfalsifiable beliefs, meaning that they can't be disproven. You can't disprove that Allah in Islam for example doesn't exist. You also can't disprove that the reason you can't believe in Allah is because deep down you actually do believe in Allah and refuse to do so. You also can't disprove that the Qur'an is unreasonable either, because it could just be that deep down you understand that it's reasonable but refuse to accept it, and are deliberately disobeying Allah. You can't disprove the existence of an evil soul that refuses to except something, because you would have to be able to observe a soul, which you can't, because it's metaphysical. These are the types of arguments Muslims make. You can't disprove that God isn't running everything in the background because you would have to be omniscient, which nobody is.
You shouldn't take unfalsifiable, un-disprovable ideas seriously, because there are an infinite number of unfalsifiable beliefs that although may sound plausible, are unreasonable to engage in. It's possible that tomorrow the sun could just randomly blow for some supernatural reason. But that doesn't mean you should act like that's the case, just because you couldn't disprove it until tomorrow finishes. `That's what the after life is. It's the idea that when you die you will go to hell for whatever reason. But you can't disprove hell, until you're dead. It's unfalsifiable, and it's ridiculous to take it seriously unless there is actual evidence that proves it's existence. What's to stop people from believing that there IS an afterlife and it exists specifically for people that believe in it? You wouldn't be able to disprove it, so does that make it true?