Personally, with things as serious as photo libraries, proprietary software is a no-go for me. I'd rather use something with community support like Lychee than pray that e.g. photostructure will be available years later.
That's why all of PhotoStructure's metadata changes are stored using EXIF or XMP standards either within the file, or alongside in a sidecar (if you prefer). File organization is also completely customizable, and designed to work in concert with other DAMs, if desired. Details are here: https://photostructure.com/faq/system-of-record/
Also: if the business ends, the code becomes open source. Details here: https://photostructure.com/faq/why-photostructure/#if-photos...
Parallelism is provided by https://github.com/photostructure/batch-cluster.js/
Metadata reads and writes are via https://github.com/photostructure/exiftool-vendored.js/
Persistence is via SQLite: https://github.com/WiseLibs/better-sqlite3
Image transforms are via Sharp: https://sharp.pixelplumbing.com/
My more nerdier blog posts are tagged here: https://photostructure.com/tags/coding/