Kagi basically just uses google search api, then does some filtering/reranking on top. (They claim to have their own index, but I've never seen it used. I've had better results using Yandex for things that i know exist but google refuses to show). I bet a large part of the perceived quality boost is just from filtering the spammy so-clones, and downranking clickbait sites. But if you're frequently searching for things that google refuses to show (either due to bias, or because they just dropped it from their index) then Kagi won't help much, just use Yandex instead.