Right now sandboxing of storage for individual apps still exists in iOS beta 13.1 from what I can tell. I can open the Files app and create a folder "On My iPad" to copy photos to but it's not as if those photos show up in any other application other than Files. Nearest I can tell they are not curated within the Photos app for example so while the files may retain their integrity in terms of their filenames they are limited in how they can be browsed/used to just the Files app.
Similarly the Files app honors the sandbox nature of curated Photos in camera roll storage so you simply can't see those folders so you can't just drag and drop your photos from SD card into there expecting them to be curated in the Photos app either.
Someone has posted in another thread where I have commented similarly that once 13 is official applications will get more access but that remains to be seen, I hope they are right.
Bottom line for me is yippie, I can copy files from external storage now . . . but booo . . i'm still extremely limited in terms of workflows . . iOS is stepping out of the way but we're not fully there yet.