Yes, it is. Bing has gotten a lot better recently. This is a good write up on indexes: https://seirdy.one/posts/2021/03/10/search-engines-with-own-...

Bing still refuses to index one of my pages, telling me to follow their rules. They won't tell me what rule I'm in violation of, though, and I can't tell that I'm in violation of any of them.

And this is educational content, text only, no ads or popups, no SEO hacking. Bing's analysis tool told me only that I was missing the "lang" attribute from my HTML tag. So I added it, but of course that wasn't the issue.

I reached out to them, and they replied saying that the page didn't meet the requirements for listing, but didn't elaborate.

It certainly makes me wonder what content their broken algorithm is missing.

And it sucks because it means DDG is missing that content, too.

No. It’s Bing in the same way that Uber is Elastic Search. It’s built on Bing and other tools and adds, tweaks, adjusts, etc. Calling DDG a Bing proxy is somewhere between misleading and dishonest.

I believe DDG uses Bing's index but has their own ranking algorithm.

They use Bing API on the background. Likely mixing in their own content.