I run a deduplication step that first finds duplicate events (AI), followed by a calculation of which event should be the listed one. It factors in description, presence of a link to the event, and having an image for the calendar feed. If you don’t like the picks that are coming out of that, you can stick your thumb on the scale. Give your definitive source a few extra points vs the big aggregator, so that their own events win if the listing quality is equivalent, or give them a whole lot of points to ignore listing quality entirely. Or penalize a source whose events come in as “better than nothing, but not by much”, so that anyone else listing the event has their version shown.
