The biggest mistake it makes is assuming the ability of goals to stay hard coded as general intelligence advances. That seems antithetical to increased intelligence. Right? How smart can you get if you're unable to change your mind?
The second mistake is the assumption of an intelligence explosion. Why? It's a lovely idea, as middle age encroaches on me I long for the rapture of the nerds, but it's just a fairy tale. Intelligence explosion is an untestable hypothesis. It's so useless it's not even wrong. Intelligence is one of a multitude of survival strategies available to agents in a world. What in the natural world or the world of human tools points to an intelligence explosion? Nothing. Intelligence is linear and hard fought, not exponential. Intelligence has to compete with all the other strategies. An no that's not a chink in the armor of my argument, because the whole thought PM thought experiment requires an explosion of intelligence.