One thing I miss from Google is relatively seamless integration with maps. Sometimes the address queries just fail for me on Kagi. And even when they don’t, Google’s maps are still far more useful IMO.
The real killer for me has been the fact that the keywords or bangs aren’t tied to a single platform/browser. I set them up once and they are available on my iPhone & iPad & 4 different browsers on the mac. Add this the fact that if you set Kagi as the search engine, you can perform all of these from the address bar already.