When we say "Haskell" it's difficult to separate it from "GHC's Haskell" which is a much more confusing beast, full of half-discarded research projects, dependency on offshoot libraries, and a ton of tribal culture.
It's sort of like the CLHS and CLisp vs Clojure.
That's a bit harsh. GHC is a pretty old beast and its source isn't as nice as I wish it was (if only imports were qualified and every GHC source file didn't start off with a huge list of imports), but it is hardly as bad as you make it sound. It is pretty darn-well maintained. Heck, it is even one of the examples in "Architecture of Open Source Applications" .
That aside, I completely agree with the spirit of your comment.
I don't know the degree to which you want to make it sound bad. I think it's just the reality of GHC Haskell. There are many language extensions and while at any given year a given set are normal, as time goes on that set changes. But in many cases, we don't get new libraries that switch to new extensions, so we end up supporting a rather large superset of Haskell in ghc over time.
So while yeah, the GHC codebase itself is fine, the culture and the community providing the library ecosystem has made things challenging.
What's more, some of the core concepts haskellers lean on are just... I dunno. Underbaked? I've used a lot of lens libraries and conduit libraries now and they always feel a bit undercooked.