I salute Swinburne for binding God to that which is logically possible. Many apologists make the claim that God is above concepts like logic and reason and I find the whole argument completely anti-philosophical. It's an apologist's way of saying "I'm right and you're wrong and there's nothing you could say to prove otherwise." It's like a kid making up the rules to a game as they go so that they always win. Logic is the best framework we have and saying that God is above logic is essentially just giving up on trying to understand how things work.
In my opinion, the problem of evil is one of the best internal critiques of the tri-omni God available. I have yet to see any rebuttal that satisfactorily dissolves it. This is no different when it comes to free will.
It's logically possible for free will to exist without evil. For example, imagine a single person who has free will but simply chooses not to sin/do evil for the length of one day. This is not that absurd. Now, imagine that they also choose not to engage in sin/evil for a second day. Now imagine that this person chooses this path for the entirety of their life. It's completely possible that this person, who has the ability to do evil, chooses not to do such for an entire lifetime. If it's logically possible for one person to do this, then it is logically possible for all people to do this simultaneously. Every single person in this scenario had the free will to do evil but simply chose not to. It may be incredibly unlikely for this to happen, but it's not logically impossible. Because it is a logically possible world, God could have created such a world. However, this is not the world we observe. This means that, although God had the option to create a world where free will exists without sin/evil, God chose not to do such. This is in direct conflict with the idea of an omnibenevolent creator.
That's not to mention the fact that God could have just put everyone straight into Heaven in the first place since he already knew exactly who would sin, who would repent, and who wouldn't. If God didn't have this knowledge, then God wouldn't be omniscient. Placing everyone on Earth first as a sort of test makes no sense because the test-giver already knows exactly what all the scores will be. Apologists may claim that the test is necessary so that the test-takers can experience taking the test, but God could have simply spawned them in Heaven/Hell right off the bat with said knowledge a priori. To claim that God couldn't do this would also be to claim that God is not omnipotent. A third strike against the tri-omni notion of God.
