Google Scholar is basically the only search feature where I have been unable to abandon Google search. If Kagi had a dedicated academic paper search engine, that would be so incredible useful. Especially if it copies Scholar's features like putting the title, authors, and year in prominent positions or (more complicated) the citation feature that lets you see what other articles cited the current one. Even if those extra features aren't feasible, any sort of journal article dedicated Kagi search would be so helpful.
So I'm contributing something new to this thread: PubMed and its associated Entrez search engine are worth looking into for APIs. It's a very comprehensive database for my field and is the best there is other than Scholar itself (for me personally).
https://www.ncbi.nlm.nih.gov/home/develop/api/