Anecdotally, clojure seems to have a very nice subset of the language which is easy to debug and expressive enough to solve most problems effectively and naturally.

What makes clojure exciting [for me] isn't the ability to build efficient transducers or create powerful custom syntax or build complicated value-level dispatch hierarchies (and in my experience, although they are cool and fun to use, all of these things certainly do make for code which is hard to understand and harder to debug), it's the comprehensive and easily-composable functional programming primitives, excellent built-in immutable data structures with intuitive shared interfaces, practical and (for the most part) straightforward approach to polymorphism, and sane approach to concurrency.

I find the high density makes debugging easier (up to a point) when combined with immutability. Being able to quickly stub/swap out a referentially transparent branch of the code while knowing you haven't more broadly changed behavior can be really useful. Also code density means you're more likely to be pointed to the line (or within a few lines) of where the actual problem is. This may be personal preference but I'd rather debug 1-5 dense line than 20-50 sparse lines given the equivalent code quality and functionality.

For me, the balancing factor is that there is much less code to debug or read.

looks like you don't know FP

pure functions are completely separate to every other parts of your software, they are very readable and easy to debug

* edit: don't write functions longer than a few lines

This. I've been using Clojure for a few years. Only once I had to actually use a debugger. Just out of curiosity.

High density?

you can accomplish a lot in a few lines of clojure