> My big issue is that doing DB-like operations is hellish in most programming languages, and if you really want to try and marshal your data into a real DB (say, SQLite or DuckDB via a library), then you have a big messy translation layer where you're trying to match things to SQL types and you have giant SQL strings everywhere.

Have heard of the JOOQ library for Java? It is a godsend because you can write guaranteed type-safe SQL using pure Java -- no syntax sugar. I expect that LINQ can do the same in C#.