This seems like you entirely missed the thread? The whole point is that this actually works for the A-series and in your made up US series it can't work because the ratio is wrong.
Let's try, start with 216 x 279 Letter and we'll scale that so we can fit two on the 279 long side, so they're just under 140mm wide now, memo size, but um, when we do that the scaled down pages are only 180mm high, even though they've got 216mm - there's a huge amount of empty white space wasted (at the top, or the bottom, or both) and that's because this ratio does not work.
Plus the copiers are a bit more clever than you give them credit for. Instead of scaling the whole page down they put a bounding box around the actual content on the pages, to exclude the margins, and then scale that down to fit. The size of the margins changes slightly but not enough that anybody cares. This is especially true when you’re copying a bound book because there’s a really big margin in the middle to accommodate the binding. You don’t need that any more once you’ve printed the pages on a single sheet of paper.
But if you really think it’s important, then you can consider a series of sizes like tabloid, letter, and memo to be equivalent to A3, A4, and A5. Each is exactly half the area of the previous, and can be had by dividing the larger size in half along the longer side.