I'm aware of the filter system and yeah spreading rumors does have a different effect but slaying a full grown dragon might be more relevant than killing a leader.
If you will kill some not related to village beast, even if it's some wild, full grown dragon who live away from civ and eating some wild boars, it's not intresting news... Killing local leader is more intresting, really.
Have you ever looked at dragons in legends?
Dragons are more bound to do stuff but his point still stands. Unless the dragon is relevant to the civilization due to doing some acts it wont matter much. Its the same with titans in my experience, sometimes they idle at thier homes for about 500 years doing absolutely nothing but killing a single dwarf or two.
What I'm trying to say is that feats of combat are undervalued in a world that seems to revolve around combat as a whole. Your point does have accurate, agreeable logic I just see it from another perspective.