The reason I like the comparison (and the "here's this giant computer and now it fits on a card that you can get at Micro Center" is another reasonable comparison) is that it deals with likeish to likeish.
It was a Mac back then - 1100 of them, but it was a Mac. You could walk into a store and buy one... or two. They might have some issue with buying a thousand of them, but they were consumer commodity equipment - it was the rack mounted version of the PowerMac G5 if I read things correctly. You might have one of them in the media lab for a high school.
And now, it's a dozen M1 MacBook Airs (or Mac minis). Still a Mac. Still something you could walk into the store and buy. But now instead of "maybe there are 1000 of them in all the grade and high schools in the state" (though that would be stretching it), its "now this is an acceptably outfitted grade school computer lab."
No regular person was ever going to get proper fraction of the nodes of BlueGene from DOE (though it was running a PowerPC 440 2C instead... but 32,768 of them) or do anything with it if they were. https://en.wikipedia.org/wiki/IBM_Blue_Gene
Comparing "that massive thing" to "this card" is impressive - but the "that massive thing" is inconceivable to the average person.
Thus the "you could have gotten a fraction of System X at a store and used it" comparison.
