I agree that list-manipulation alone is too broad, but list-filtering will eventually suffer from the same problem as well. I think the problem here is that while list-manipulation is a perfectly good umbrella tag for such questions, most users don't use additional tags to narrow down the scope (or if they do, they use/create highly specific tags).
A solution would be to use secondary tags such as sorting, gathering, duplicates, filtering, etc. in addition to list-manipulation. I like this solution because
- it automatically categorizes these questions using common and well known search terms, rather than a new tag which someone might not know about. Searching for these questions is easy, since the results returned are the intersection of the sets (tags).
- it can be used for other combinations, such as string-manipulation+sorting or signal-processing+filtering, etc. without having to create localized tags such as string-filtering or signal-filtering, etc.
I think this is one of the strong points of SE's tagging system, but in practice, it's not often done this way. Users might use only one or the other and it's up to the editors of the site to retag appropriately (e.g. a question with just filtering should not be left as is).