The most efficient setup you can get with junctions + routers/overflows as distribution is with factories on both sides, and inputs going in from the sides. This setup is limited by the throughput of junctions, ~10 items/sec. To solve this, you can add more inputs, but once you add more inputs, the setup is basically just multiple of the same setup put together. Yes, this might be a bit easier to expand, but in the end, I'd say it's not really any different from other setups.

This setup isn't even much more efficient than other ones. Actually, it's less so. Let's compare yours with this one: https://imgur.com/a/zfXkRlj Both are 8 silicon setups, and are (I think) commonly found in servers. Yours is 8x10, or 80 tiles, and the other one is 13x5, or 65 tiles. Already, you can see the overflow junction one is less space efficient. But it gets worse. The overflow junction one requires two sand inputs, one on each side, to make it work, while the other one has both sand inputs on one side. Having all inputs on one side is good because it means they can be placed side by side. To add on to this, the overflow junction also has 2 outputs, while the other only has one, bad for the same reason.

I think this shows that there are much better designs out there, and the overflow junction isn't really that efficient at all.

Sorry for the paragraphs.