Forest for the trees, I already practically doubled my numbers and assumed McDonalds gets all their orders in the same 8 hour period! And even then multiplying

Forest for the trees, I already practically doubled my numbers and assumed McDonalds gets all their orders in the same 8 hour period! And even then multiplying them by 100 doesn't get you into the realm of "we couldn't build this on a monolithic horizontally scaling application". If anything, if you're at McDonalds scale and still can't find the engineering skill to build a monolith that can handle 30k operations per second, you're playing with fire building a distributed system. (if you're a nascent startup, then by all means stand on the shoulder of giants and don't sweat that you don't have a full blown cloud engineering org, but that's definitely not where McDonalds should be...)