StreetComplete is fairly limited in scope (which is a good thing, considering its focus on UX and doing that single thing really well).

But there are a bunch of more “expert” features, such as the overlays, which allow for more focused QA work. And there's also a way of recording a GPX trace for missing paths or streets that will be added as a note for others to add to the map (or yourself, just not from the same app). Just long-press the screen and you can start such a recording.

With the places or things overlays you can also add new POIs in a limited way. It's still not a full-fleded editor (and as mentioned before, I think it shouldn't be), but there are now ways of doing more edits that were not possible previously, while not altering the interaction that much.