Even if every possible event had a particular root cause it could be reduced to (and I think that assumption itself is oversimplifying things vastly), the relationship would not mean any given event is predetermined. You are ignoring the effects of randomness and aggregation of randomness. Your view is equivalent to assuming that if a coin was flipped and has landed tails, it has always been so predetermined, but we know that the chance of that has always been 50%. It seems to me that if we take your view to it’s logical extreme, there would be no motion in the universe, no change even on subatomic level, no evolution or growth - it would be an inert static thing, as there would be no initial root cause to trigger any change that would cause further reactions.

(on a personal level, if you seriously feel this way and want to talk, feel free to email me, aeontech at gmail).