I feel like I get the author's points pretty well. I had in fact chosen Terraform when it was newer as a greenfield project to deploy our infrastructure more quickly at another company. And I was happy to find out my current company had built all their infrastructure with Terraform, since by that point I knew it really well. But I still struggle with interacting with it, expanding it, and trying to get it to sing to me.
The example given is pretty good at demonstrating how Terraform itself has some unique problems that they themselves created: using counts for enabling/disabling resources, using locals as proxies for data comprehension, writing long-ass resource descriptions, often with built-in functions and ternaries to get it to do what you want in various scenarios. Trying to be DRY in Terraform can often be a chore. I think Terraform's MO is actually that some duplicate code isn't the worst thing, so you end up with piles of duplicate lines that are extremely difficult to read, and where writing a function would be super helpful. We had an engineer do a bunch of Terragrunt work for a project and I found that code nigh-incomprehensible.
So, I get it as well, I get where they're coming from.
I also think working with DSLs isn't a huge waste of time, since many of the things we work on are abstractions of abstractions. It seems like everything I'm doing today is probably going to go away in due time, but I know how to program, read docs, and pivot quickly. I do feel like as long as you're gaining an understanding of the underlying elements, your time spent in a DSL (assuming you're getting paid or you end up using it for several years), is still well spent.
They mention Puppet, and I remember getting a job offer once because I was able to read the Puppet documentation and write out a little script that could do the ask in Puppet, even though I had never used it in a professional capacity before. It was easy to pick up and I would've happily worked in it if I accepted the offer. The knowledge I gain around deploying to AWS or other cloud providers is often transferrable in that manner too.
The clouds themselves are a sort of DSL often, but I can't say that my time spent with Azure was a waste just because I'm working in AWS now. No, we delivered stuff on that platform, I learned its pros and cons, I gained some wider understanding of what cloud platforms could do, and I got paid along the way :)