I've asked a number of times on HN threads for specific examples of searches that Kagi performs better on than DDG or Google, and never gotten a solid reply. It seems what people like about Kagi is the customization and surrounding tooling, but the actual search quality is about the same or possibly worse. That's cool, but I don't find it worth the cash personally.
For me the quality of results is improved exactly because of the customization. Removing sites which I don't trust, are low quality, spammy, etc.