I've been on several sides of this issue. I've been using Haskell for around 16 years, and I currently work on a product that's written almost entirely in Haskell on the backend. I've worked in a variety of languages throughout my career, and I've taken plenty of jobs that involved no FP at all, jobs that involved a mix of languages, and some that were primarily Haskell.
I've certainly seen people in the Haskell teams I've worked on who fit the article's description of people who were there to write Haskell and didn't care about much else. It didn't go great, but they were a minority of the people I've worked with.
Importantly, I've also seen plenty of that kind of behavior in other teams using other tech stacks. I've worked with "Agile people" whose answer to every problem is pair programming. I've worked with people who only care about microservices, or their favorite frontend framework. I've worked with people who see more object orientation as the solution to every problem more often than I've seen people who want to apply FP to every problem.
A few of these people can be find to have on a medium or larger sized team- if the worst of their instincts are tempered they can be a great source of internal education and advocacy, and they can bring expertise that can help you deal with the inevitable problems and tradeoffs that come with any technical choice. You just need to be careful to, on balance, have a team of mostly product-minded people.
Product people aren't necessarily tech-stack agnostic. To use myself as an example, I really like functional programming and I think it's often a good technical choice. At the end of the day though, my job is a job and I'm there to build the best product I can to make my employer (and myself) money. I've turned down Haskell jobs because I didn't believe in the product or team, and taken jobs in less preferred tech stacks because I did. A lot of people can be both enthusiasts and pragmatists, you just need to look for them.
I think one of the biggest issues I have with the article is that it overlooks a significant source of hiring: product minded people who are open to, but not specifically enthusiastic about your tech stack. People don't need to be an FP enthusiast to work in a functional language. I've written a lot of Python and Go in my career, even though neither of them are my favorite language. By the same token, there are plenty of people who can work with Haskell, OCaml, or a lisp just fine with a bit of training even if FP isn't something they are going to devote themselves to. I've worked with a lot of people who do Haskell in their day job, but prefer to spend their free time using Rust.
None of this is to say that everyone should go out and use an FP language. I think the most important factor in picking a language is generally going to be picking something that your team likes and understands well. Most languages are good enough at most problems that individual preference is going to matter more than technical concerns. If Haskell or OCaml or Gooby is that preferred language for your team, I don't think you should avoid it.