This is true IFF you get to the point where you have to split up.
I know we're all hot and bothered about getting our apps to scale up to be the next unicorn, but most apps never need to scale past the limit of a single very high-performance database. For most people, this single huge DB is sufficient.
Also, for many (maybe even most) applications, designated outages for maintenance are not only acceptable, but industry standard. Banks have had, and continue to have designated outages all the time, usually on weekends when the impact is reduced.
Sure, what I just wrote is bad advice for mega-scale SaaS offerings with millions of concurrent users, but most of us aren't building those, as much as we would like to pretend that we are.
I will say that TWO of those servers, with some form of synchronous replication, and point in time snapshots, are probably a better choice, but that's hair-splitting.
(and I am a dyed in the wool microservices, scale-out Amazon WS fanboi).