When you have a mix of file types (some reports might be in DOC, others in PDF, etc...) then having to open those files through their respective application is tedious. I find it much more efficient to simply hope into File Explorer, navigate to where I know the files are and open them from there. I don't have to think in advance about what type the file is.
That's not what I meant. You use the app native to the source, not the file type. For example, I use the Google Drive app to navigate Google Drive. If I had Dropbox, I'd use the Dropbox app. Those apps are tailored to those services, and match the experience users will have with the web versions. Local files are stored in downloads, and Android ships with a download manager.
Maybe you'd rather have a single app manage them all, but that's a subjective preference (and one you can still easily fulfill). It is not objectively better.
This is why I've always held the position that Android generally provides users with a fragmented, inconsistent experience - browsing for files while in the process of attaching them to an email is done through a different application/interface than opening files for viewing on the device.
If you can't figure out the document manager, you're not going to be able to manage any kind of file explorer. It's about the simplest app/interface imaginable.
I find it humorous that those who made fun of BB10 users having to take extra steps to get apps such as using "Snap" are now advocating that the additional steps to get a file manager onto their device suddenly constitutes "choice and customizability".
There are two huge and obvious differences here. The first is that the Play Store ships with every Android phone with Google services, and using it to find apps is an expected use case for which the phone is designed. Side loading a third party service in order to gain questionable access to the Play Store was not something BlackBerry intended when they designed BB10.
Secondly, the average user will never miss having a file manager. Like I said, I haven't used one in years, and I use my phone for work purposes regularly - the document manager does the job just fine. People seem to manage fine with iPhones. On the other hand, I think the average user will miss having access to a robust app store.