Step 4 is not at all obvious and would require some significant justification. General intelligence is, well, general. My primate brain may not be able at all

Step 4 is not at all obvious and would require some significant justification. General intelligence is, well, general. My primate brain may not be able at all to intuit what it is like to move on a 7-dimensional hyper-surface in an 11-dimensional space, but thanks to the wonders of formalized mathematics I can work out and tell you anything you want to know about higher-dimensional geometry. If the super-intelligence itself is computable, and we have the machinery to verify portions of the computation ourselves, it is in principle understandable. Of course there will be computational limits, but that's hardly anything new. There is no single person who can tell you absolutely everything about how a Boeing 787 works. Not even the engineers that built the thing. They work in groups as a collective intelligence, and use cognitive artifacts (CAD systems, simulators, automated design) to enhance their productive capacity. But still, we manage to build and fly them safely and routinely. There is no law of nature which says that human beings can't understand something which is smarter than them. Deep Blue is way smarter than me or any other human being at Chess. But its operation and move selection is no mystery to anyone who cares to investigate its inner workings.