I LOVE that Kagi allows me to higher and lower a websites ranking. It is a MAJOR reason why I am using it and why I plan on paying for it. Never stop. However, I left Google because of the filter bubble and censorship. Once you start increasing the ranking of many websites you love and you combine it with the fact that that Kagi limits the amount of search results that show up, you can easily get a list of search results only consisting of websites that you've previously visited. The more you use the boost feature the less unique websites you've never visited/seen before show up! I agree that if you have to scroll multiple pages to find something then the search engine has failed, however even though the boosted websites are amazing for the user, it limits the amount of new amazing websites that they can come across the more they use it! It can be argued that it's even worse than Google's filter bubble because the boosted sites the user has chosen are amazing ones that they don't mind seeing and thus unlike Google's bubble, they have no motivation to hate the filter bubble.
I propose a simple solution. Some more search results would always be nice but more specifically, at the bottom of the search results, there should ALWAYS be a dedicated section of 2 or 3 links that are completely unique that have not been boosted. This way no matter how many sites a user boosts, they will still be exposed to new websites/views.