Having just recently made the move from Android to iOS, I think I can help with that.
In the example you gave of moving music from the ICloud to your IPad you were working within that Apple Eco System so everything went as expected and worked fine. Those of us coming from Android are use to seeing, and having access to, all of the files on our device in a structure very much like we would on a PC. If I wanted my music files on my Android tablet to live here: "\\Todd's Stuff\Offline Music\Artist\Album" it would not be a problem. I could copy my music to that folder (maintaining the /Artist/Album sub folder structure) and then point any music App I wanted to those folders and it could play the music. Same thing with photos, movies, anything, store it where you want. With iOS Apple assumes that I want all of my photos and movies stored in Photos, no other option. So I think when people say "there is no file explorer" (I didn't say it) they mean that the "Files" App does not give them nearly the control or flexibility that they expected.
I suspect the difference comes down to Apple's "It just works" philosophy. Don't worry about where the files are, we'll take care of that. Just use our Apps and everything will be fine.
I think both systems have advantages and disadvantages. I still miss some things Android, but I am not headed back. Also I think Android is headed down a path that will lead to less flexability to improve security. And Apple is quite aware of the frustration of some of its users concerning the iOS file system, they are planning to do some changes with iOS 16. Fingers crossed, we get some additional flexibility.