Facebook, Twitter, and Google all started simple and scaled only when it became necessary. If you want to do what they're doing, start by doing what they did. Don't skip to the microservices.
The right approach is to optimize for speed and flexibility. Make it as easy as possible to validate your idea. Make it easy to tear down and rebuild in a "scalable" way if you're lucky enough to make it past step #1.
Also, the overwhelming majority of companies that claim that they need to scale into the millions of DAU will never make it there.
I think it might be more efficient to do whatever is fastest/easiest based on what you know now & always plan on refactoring when you know more. So you end up trying to write less, simpler, code knowing you're going to tear it apart soon.
Which I think still fits with your overall point.