Being boring has nothing to do with scale. Some of the biggest applications run on incredibly simple architectures, and often are able to scale so well because of that (boring) simplicity.
Definitely not. I'd much rather scale Postgres manually through layers of sharding and proxies than handle Cassandra.
There is ScyllaDB for a much better reimplementation of Cassandra/Dynamo, but wide-column databases are still best for niche scenarios, especially as RDBMS are rapidly evolving into natively distributed architectures.
Monolithic apps running on big servers talking to databases running on big servers. Very little orchestration overhead or complexity with serverless and the rest.
Everything from StackOverflow to ad serving systems to high-frequency trading exchanges are run this way.
What is your definition of non-boring architecture? I'm curious as to what you consider the exciting architectures necessary for scaling to make sure we're talking about the same thing.
Quora, Pinterest, Twitter, etc are all just big app instances talking to DB instances, with separate systems for background processing, queues, and caching. Are you suggesting that they would scale better with serverless functions instead?