I don't understand the reasoning behind Kagi developing a browser. Such a small team would gain more from partnering with the likes of Mozilla/Vivaldi/etc IMO
Browsers being broken is very closely related to Google/search being broken.
I assume it's the same reason that Google decided to develop its own browser
Firefox uses Google as the default search engine, Vivaldi goes with Startpage. I doubt either would change to a stripped-down version of Kagi. Because that's how this would most likely be done, and Kagi wouldn't get much of such deals.