I feel that perhaps you are operating on a different definition of unpack than I am. For me, "can be good at everything" is less evocative than "achieves its value when presented with a wide array of environments" in that the latter immediately suggests quantification whereas the former uses qualitative language, which was the point of the original question as far as I could see. To be specific: Imagine a set of many different non-trivial agents all of whom are paper clip maximizers. You created copies of each and place them in a variety of non-trivial simulated environments. The ones that average more paperclips across all environments could be said to be more intelligent.
You can use the "can be good at everything" definition to suggest quantification as well. For example, you could take these same agents and make them produce other things, not just paperclips, like microchips, or spaceships, or whatever, and then the agents that are better at making those are the more intelligent ones. So it's just using more technical terms to mean the same thing.
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.