Despite I don't expect you to try it, I want to know if I use a library like this, and when I use the static meshes of each geometry and feed into there.

The calculation didn''t take much time, but if I break down the frame hierarchy, let's say, I had 67 submeshes and feed into there again. It would generate 500K cells, which takes forever to complete

It just takes a lot of time to precompute, how to save me a dozen on this if I use flattened frame hierarchy?

https://github.com/fredericjoanis/Argorha-Pathfinding

did you try Recast? Even the author of your project says it's better (no experience myself).

This library does have some advantage over recast in certain scenarios, such as the ones that when you need HPA to work with. In recast, it doesn't support HPA or it is very hard to achieve, as suggested by the author, when you have a fairly large extent as large as  the global or a continent, it does give you an edge from this library.
Thanks
Jack