If you need USB 3 speeds, I almost never plug my phone in other than to charge. Maybe it would be nice for backups...but I just use iCloud. For the iPad Pro it would be nice to transfer files onto it, but you still have to go through iTunes so I tend to avoid that.
Are you using the same iOS 9 as I am? Because Apple's system of "Open In..." generates endless copies of files, with no way to properly manage them.
Take this incredibly rudimentary scenario. I use two apps to edit a file (Because one is good at one thing, and another is good at another.) We'll say we are modifying a PDF file.
- Use dropbox to "Open In..." app A
- Edit inside of app A, "Open In..." app B
- Edit inside of app B, "Open In..." Dropbox
How many copies of the file are there now? The answer is 3. Dropbox has the latest copy, App B has the latest copy as well (identical to the dropbox version, unless you edit it on another machine) and app A has an outdated copy missing changes from app B edits.
In what universe is this simpler than having App A and App B able to access the single copy of a file on dropbox?
And lets not get into the most obvious downfall of the iOS "file system", lack of external storage options.
I own an iPad Pro and I love using it, but it is years away from being able to replace a laptop for me, even for my hobby of photo/video editing. Primarily because of how difficult it is to move data to/from/within the OS.
The problem is that Apple already have a solution for it but it's opt-in for apps. As I mentioned a few times, it's called Document Picker and lets you use the same file in various apps.
Also, _Open in_ is supposed to copy the file to the app's sandboxed container, so the app can work with it since it cannot leave its own container. That's intentional and if the app was updated to let you use Document Picker, it would've solve your problem since iOS would become the manager for the files.