As a counterexample, I searched for something very obscure (only three pages on startpage) expecting to see them pulling in results from startpage to cover the long tail. I was surprised to see different results, suggesting their index is much larger than I assumed.
The query was "retail snap incentive program"
Edit: All your queries are for relatively popular terms. I wouldn't be surprised if there's just a clearly right top set of pages.
> I wouldn't be surprised if there's just a clearly right top set of pages.
I would be astounded! Why would DDG, Bing, etc. not use it? Different search indices and engines should practically always have differences in results, as ranking results is very fuzzy and dependent on the available data.
90% of queries being identical to Google but different from the 25 other independent engines is one hell of a coincidence.
Archived example:
Brave results for "gccgo": https://web.archive.org/web/20210622172743/https://search.br...
Google results for "gccgo" (proxied through Startpage): https://web.archive.org/web/20210622172939/https://startpage...
If this is a bug, it's very serious and needs to be publicly disclosed.
Edit: more examples:
Brave results for "oppenheimer": https://web.archive.org/web/20210622173647/https://search.br...
Google results for "Oppenheimer" (proxied through Startpage): https://web.archive.org/web/20210622173658/https://startpage...