There seems to be a growing consensus around the idea that alternative search engines aren't viable without their own browser. Cliqz (acquired by Brave), DDG (obviously successful by some metrics, but not a real threat to Google), Kagi (pops up from time to time here)[0]. Given that Google considers it worth tens of billions of dollars a year to remain the default on Apple devices and Firefox, the default search advantage is clearly quite important.
I'm not sold on the idea that convincing people to install a different browser will be easier than teaching them to install an extension or choose a different default search provider, but clearly the latter isn't paying off.