I would argue the most important “thing to add” here is a business model and company structure that actually benefits from this complexity. There are indeed bus

I would argue the most important “thing to add” here is a business model and company structure that actually benefits from this complexity. There are indeed businesses and large teams that benefit immensely from well-thought-out architectures such as the one you describe. Most internet businesses, though, just need a single service deployed across two or more availability zones, that talks to a SQL database with one or more hot standbys. Once that basic architecture stops working, you have good problems.