I'm like you, and a big fan of Pigallery2 precisely for its simplicity. But it turns out that Immich does support external libraries, so you can keep your manual file management in your filesystem and still use Immich for efficient indexing, face recognition, quick picture retrieval by year, location, people etc...

I'd recommend you try Immich (there's a docker compose version) and if you don't like it, you can just remove it and move on.