I've tried many times to learn Haskell. The problem is always with setting up a compiler, getting packages, setting environment, not getting a ton of gigabytes of duplicated packages, getting useful vim support etc.
How does stack help here?
In the end you still might have duplicated dependencies if you use different stackage.org releases but it's a much better situation than using Cabal sandboxes where every project has its own copy of dependencies.