Completely agree with you that Kagi e-mail will be unnecessary, even though I trust them on privacy. There are already great e-mail providers, such as Fastmail. But it makes some sense for them to go for e-mail, since they're already hitting Google on search. They're basically going after Google where it's possible: search, web browser, e-mail. They can't go after Google on maps or video streaming, so they do what they can. I'd much rather they innovate and get ready for the future of the internet after AI has destroyed traditional discovery.
The reason people use Google Maps is because businesses provide them with their opening hours and users provide them with reviews, photos, etc. A small company like Kagi can never have that (unless they buy it from Google), so they can't really compete with GMaps. Apple could have a shot, if they weren't so arrogant.