As someone who has legitimately tried to use Bing let me just say, Bing's issue isn't its lack of indexing. Every time you search on Google you're "teaching" Google's system what results you'll most likely want.

So for example if I search for "that movie with dinosaurs" on Bing and Google, Bing's no.1 result is an IMDB link to a movie called "Dinosaur (2000)." That's not a "stupid" suggestion, but it is still not how people use search engines. Google shows me "jurassic park" and "the land before time" neither of which contain the word "dinosaur" in the title.

That's because millions of people have likely searched "that movie with a dinosaur" and clicked on the "Jurassic Park"/"Land Before Time" links. This information cannot be gained by simply just indexing no matter how amazing your indexer is.

So let's say, theoretically, that someone stole Google's code. They then reproduced Google's infrastructure, search algorithms, and so on but WITHOUT Google's massive database of historic queries. I legitimately do not think that this company, even with all of Google's stuff could catch up with Google, because 1. Those historic queries now ARE the core of Google's results, and 2. Google will always out-pace the competition in generating new intelligent results (due to more usage).

It is a circular problem. Bing could be twice as good as Google under the covers, but it will never catch up for the reasons I said above... Ditto with DDG or anyone else.

PS - As an aside, Google's search query parsing is significantly better than Bing's when it comes to programming/technical queries. Every time a quote appears in a bing query it treats it as a literal query string, Google seems to understand the context of the double quote (i.e. that it was from the source material) and give you non-literal query string results.