I never went into why FP is better. I only said I believe it is better and that composition lies at the heart of this differentiation. So you are offering an opinion on something that I haven't expanded upon yet.
Allow me to explain why I believe composition in FP is a "better design" than other paradigms. First let's get on the same page about the true nature of design. What is it? I talk about it here: https://news.ycombinator.com/item?id=21953290
Once we're on the same page on what is design in general you can read about why I believe FP is better in general. I posted on quora, a definition of "good design" in the context programming and program organization. Then I go into why FP under this definition is "better."
https://www.quora.com/Is-senior-full-stack-engineer-Ilya-Suz...
The answer is not straightforward and I get into the caveats in the comments on that quora post.
I believe the definitions for design that I am describing are universal and concretely illustrate what we all talk about when we talk about "design." If you have a different definition of design than the problem is just semantic in nature. At the very least I think we can agree that in terms of this definition of "good design" FP is the better than OOP and imperative.