Re: The stagnation of Science and Technology. We've seen such stagnations before in history. Our culture has been losing the idea of science as a process of increasing understanding through inquiry. As expressed by the mass of people, the culture has been going towards a cargo cult worship of science. Western culture once enshrined the erroneous conclusions of Aristotle, instead of engaging in his act of inquiry.

Re: The particular exception of computers. If there were something like a PAIperclip Optimizer, it wouldn't be trying to produce paperclips. Rather, it would be producing something which is highly sought by virtually every person, most of industry, and every sector of society. If there were something like the PAIperclip Optimizer, we would see outsized progress in one particular area, focused around the production of the optimized thing. A super-optimizing AI wouldn't try to kill us off by firing off our missiles. It would instead warp our culture, so that it's producing the optimized thing.

Given that self preservation is such a strong, foundational behavioral pattern, the optimized thing would obviously be more and more faster and faster computers.