Why wouldn't Apple accept a payment for bringing billions of dollars in traffic to Google?
Google pays Apple to set it as the default as its a positive sum to both sides. Google gets more than $15bn of value from the traffic and Apple gets $15bn for the obvious decision. Google could call Apple's bluff and refuse to pay, but Apple could pull through on their threat to replace default search with an inferior engine. They did it with Google Maps by replacing it with Apple Maps, which was a widely unpopular decision
But answering your question, it could let the user choose their search engine as part of the onboarding experience while providing a random preselected default.
Google are paying tens of billions to keep them in the "default" dominant position because they know this.
For my usage it gives good results, and it has the added bonus of providing links to google et al when you scroll down the results (it assumes that if the first page of results isn't good enough then the user will go elsewhere, so why not provide links to the other search engines?).
(I don't like their font but that's an easy fix with userstyles.)