I agree that both the map and the statistic I've posted don't take those country-specific characteristics into account.
I'm not sure how important that difference really is, though, as both the US and Germany seem to have pretty similar degrees of urbanization (US: 83.3%; Germany: 77.8%; source). So the rural population isn't really that big in either country, relatively speaking.
I'm not trying to say that the rural population isn't a factor, I'm just not sure how big that factor really is.
I‘m personally very happy with kagi when it comes to features and, most importantly, the quality of search results. But, as they don‘t have ads, it’s pretty expensive to use.