I completely agree with your long assessment of the files app. It’s the claustrophobia of not being “allowed” to bring in a file— or store it, or manage it in iOS that makes its such a frustrating and limp creative tool.
I’ve spent a lot of time using the iPad Pro 10.5 and its absolutely brilliant at a lot of things (especially with the pencil), and it appears to show tons of promise for future tasks like video editing, and so on— but Apple’s strangely closed off ecosystem looks like it might choke off real innovation as it relates to truly creating with (and collaborating) on important work.
I don’t want to own or use a Surface tablet, but without a way to create, move and organize common media files, that may be the only option. Such a shame.