I'm having similar requirements as you - coming from an organically grown folder structure on a PC, the photos app on iOS & Mac does not give me sufficient options to mirror this structure. What I do is to use a different cloud service (Onedrive in my case), which works like an extension of a PC file & folder structure, which can be accessed on iOS like a hierarchical structure on a PC. It also synchs new pictures taken with your iPhone, if you want, and you can move them to any destination folder you like afterwards. It also synchs back to the PC if you want it to do so, of course.
On top of the 'regular' folder view, it also offers a sequential photo 'stream' view, similar to Apple's, where you can organize pictures in albums etc. (this does not affect you 'PC' folder structure though).
What I miss ist the iOS picture app AI features like analyzing picture content and faces, allowing you to search for certain things & people, even without having tagged them with keywords previously. This sometimes works like magic (not always though). I'm therefore keeping pictures in the iOS app, on top of synching them with Onedrive, in particular newly made phone pictures - as long as storage lasts.
This is what I do. I'm sure there are other ways to get to what you need.