The design space of "heuristics soup" is much larger than the space of "clean designs", which gives the "cleanly designed" FAI approach a speed advantage. (This is my guess of why someone might think "cleanly designed" FAI will win the race for AGI. Somebody correct me if there are stronger reasons.)

Whaaat? This seems like saying "the design space of vehicles is much larger than the design space of bulldozers, which gives bulldozers a speed advantage". Bulldozers aren't easier to develop, and they don't move faster, just because they are a more constrained target than "vehicle"... do they? What am I missing?