I'm assuming they already are using the package manager. The issue is that there are so many dependencies for a single package, and almost every system update consist of updating a bunch of Haskell packages which just clutters maintenance.

Distribution does it job: it distributes upstream changes. It's like blaming a zip file, because it contains many small files instead of a few big, so it clutters maintenance. If you see this as a problem, then fix upstream. For me, it's important to receive all upstream changes in one update.

You still could. With proper build systems they could be pushing a new package whenever a dependency gets updated, or daily.

Daily would be a huge improvement but preferably less if it is non critical and I am not using testing repos.

No, I didn't. But, before uninstalling Pandoc, I was wasting time with frequent useless updates of minor Haskell dependencies that should be statically linked in the first place as no other package, at least in general, make use of them.