I‘ve seen it mentioned a few times as being superior to the iD editor but the learning curve seems somewhat steep. I started mapping areas in Vietnam that haven‘t gotten much love so far and I encountered a few limitations with the iD editor. The buildings in Vietnam are a pain to map. Is it better in the long run to learn JOSM for this use case?
Yes. JOSM is pretty much the default editor for serious mappers, by far the one that most effort has gone into to make it powerful.