Likewise with the doubling of nodes, this is obviously a blue-green style deployment. In place updates would be quicker but ES can get into all sorts of weird states that require manual debugging to fix, with blue green for most of the deployment you can simply flip back.
I've been pretty impressed with AWS ES compared to running it myself (other than the poor fit of IAM auth)
If this is a reality of using cloud based ES then clearly it's something to seriously consider before using it - which is all the author is saying. The article is titled 'things to consider' not 'things AWS needs to fix'.
ES is big complex beast of a Java app. This is good advice regardless from someone who has used both approaches (self hosted vs AWS) in production.
I did not get the impress that he's saying that AWS can resolve this easily.
This is a bad assumption. Loggly is a shared service.
> Any API that AWS ES exposes has to be there forever
This a bad assumption. No API is forever. Maybe you meant a different timescale. AWS has removed and made breaking changes to APIs over the years (e.g. random breaking change: https://forums.aws.amazon.com/message.jspa?messageID=513640).