This is not an argument against static advertisements:
If an ad-free service is willing to introduce advertisements of any kind, regardless of what payment tier they are served to, then said service is no longer ad-free.
This is also a slippery slope to dropping standards for even the highest-paying users, as has been seen countless times, most notably in "ad-free" streaming services, of which there are now none left, as even those that don't play mid-roll ads plaster advertisements across their service for even premium members.
Also, Kagi's whole mission is about being responsive to users, tracking-free, advertisement-free, and censorship-free*
*this has previously been upheld in Kagi's refusal to censor search result categories some may be unable to handle, whether or not for good reasons