Haskell probably has a long road to mastery. That said I think it might still be shorter than that for C++. it is hard to think of a language that takes longer than c++ to master. Interesting!
Fair enough. I found haskell easier than c++ to grok. It may have helped that I had a good grasp on type theory before I learned Haskell (worked through TAPL a few years ago). Subjectively, I found the various components of Haskell almost always fit together in very logical fashion with a very clean syntax, while C++ felt arbitrary, (with exceptions to every rule and exceptions to those exceptions and exceptions to those). I share your intent of not starting a language war. Just expressing my experience.
Of course, there can be no objective measure easily made, and I do not want to engage in language wars.
That said, I am a C++ expert, but contend that each of Lisp, Haskell, and Scala are far deeper languages, with more involved in their mastery than C++.