Then, of course: "You're using the service wrong, silly, all you have to do is sign up for a few years to a bunch of our services".
proceeds...
Don't be fooled, AWS and the likes are very expensive, not as much as Heroku, but definitely more than OVH for example.
I am currently migrating a client's (valuable) production from AWS to OVH to divide their infrastructure cost by 3. Thankfully it did not depend on any non-OSS parts (RDS becomes a Postgres etc).
The question becomes: how far can you go with serverless until you have to move out, and then how much money was really saved once you paid the price of un-aws-ing?
The author of the article clearly spent quite a lot of human ressources and money to get his serverless setup running (hosted ES, Kibana, etc gets expensive fast).
In the end, I find it hard to believe that this is a real time saver, let alone a money saver, in fine.