I think with billions of dollars in funding they could accomplish a "good enough product" in 5 years personally. They don't need to be as good as google.
Hard to be the quality leader in the market when your customers find your software inferior.
Apple has been indexing the web for years, using that for Siri and Spotlight search results. They continue to make improvements to their search capabilities in plain sight.
https://support.apple.com/en-us/HT204683
You can safely assume that for any critical external dependencies, Apple is working on one or more Plan Bs.
Today I guess one can have more than 50 times the compute capacity at around the same price and in way smaller space. (Estimating from Moores law.)
Given that Google has been lowering their quality over the last 10 years it shouldn't be that hard to compete from a technical perspective.
It’s not like Apple to not control everything, but they could do something similar to alleviate the effort in the tail end.
They could buy another search engine, but again getting Duck Duck Go to scale Google scale and relevance is still honestly a massive project.
I think they would risk losing people to Android phones as well. If tech-illiterate people suddenly start seeing that the "search engine" in Apple is terrible compared to Android they could lose customers. Better to just keep taking money, have a great search experience, and focus on other things.
I'm curious, can you share which one?