People in tech circles always say DDG has a crawler. I know they do. No one ever says how big it is. I have a hard time believing it’s crawling more than a couple percent what Bing is crawling.
One complicating matter is that it specializes in DDG's "Instant Answers"; apparently¹ the "source from other search engines" approach really only applies to the traditional results list, while DuckDuckBot is focused specifically on the Instant Answers, effectively optimizing for the absolute most relevant first result possible. So in its current state DuckDuckBot ain't exactly comparable in purpose.
Still, I don't see much that'd be stopping DDG from ramping this up and having it generate the traditional list of results, too. Yeah, obviously the results for quite a few queries will be far from ideal, but if the query already hits one of DDG's curated data sources, I suspect the results might already be better if anything.
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¹: https://help.duckduckgo.com/duckduckgo-help-pages/results/so...
If all the users go to DDG.com, it won't matter if Bing has a great backend or not.
I've recently lived this experience in another context. We built a great backend for a partner that was good at publicity. When they redirected users to their internal backend, we were dead in the water. It didn't matter that the partner struggled with their backend and ours was better. We hadn't invested resources in independent publicity, so users couldn't find us. It was a hard lesson to learn.