It allows access to a filesystem, just not the root filesystem.
You can do all the basic copy/cut/paste ops and create whatever folder structure you want. Don't expect to edit system files though. People spend lots of time looking for vulnerabilities to achieve that.
The iOS file system is very frustrating. By default, applications can only access individual files in their own sandbox, and if you want to point an application to a folder of media, you can't—it's simply not possible, or if it is it's so burdensome that it's simply not practical. Least of all for images, which for some reason are not accessible from the Files application and have to be manually exported from the photo gallery app, and music, which is not accessible at all: you need to clumsily use Apple's proprietary sync program on an actual computer.
In contrast, Android also doesn't let you access the root file system, but the user folder is yours to do whatever the hell you want with, and if you want to give your audiobook or music app to your folder of mp3 files that you've collected over the years, you can.
You can do all the basic copy/cut/paste ops and create whatever folder structure you want. Don't expect to edit system files though. People spend lots of time looking for vulnerabilities to achieve that.