The new update (to Moodle 3.8) includes some strong improvements to the core forums which bring it much closer to the Open Forums tool. Advanced grading and the summary reports in particular really help close the gap. The things that are maybe not quite there are related to accessibility and the grading workflows. The new release is worth checking out. We (Open LMS) are not quite ready to tell people to think about switching away from Open Forums but that day is believable now in a way it has not been.
An advantage of using the core forums is that they work natively with the mobile app.