No offence intended, however, this is literally the pitch I have seen for why startups with 5 users need to architect their product to be global scale for 1 billion concurrent users. (those that try always burn out and fail)

In reality, I feel like this tends to translate to "we need to scale horizontally and make sure our code runs on a large number of machines" with little consideration for actually optimizing the code itself.

In fact, devoting time to code optimization tends to be explicitly discouraged in my experience. The prevailing wisdom seems to be, "write shitty code... just make sure it runs on as many AWS machine instances as possible."