So what happens when someone shares a one drive document with you via your email address? What accounts gets it (the MS account or the 365 account)?
I suppose, the email will reach me via the domain-linked account: business account. If I am logged out at that moment in my browser, I’d expect it to ask me to log in and then that identity would get the file. Maybe the link is clever enough to know that the file is meant for a specific account - not sure. I’ll let you know once it comes up! 
Complex technical documents are often worked on by teams who can be a mixture of company employees and external specialists, sometimes in different countries, all making their own contributions in the form of embedded comments and edits.
I’ve been working in that environment even before Office existed, and having everyone using the same product for editing shared documents is the only way to ensure things don’t get mangled. As an external contractor I will sometimes be working on a client-supplied system, sometimes on one of my own (new install of Windows, only programs required by the client, no use outside of that client’s work, before anyone says anything).
Having an Office365 account is my way of ensuring I’m always using the same software as the client, and it’s up to date and fully patched.
The need to use Office is greater if the client’s Word documents switch between landscape and portrait page layout multiple times in the same document, and becomes essential if they also include embedded spreadsheets, presentations or PDFs. My experience with things like Open Office and Libre Office suggests that they are ideal for personal and small/medium business use, but don’t have the level of sophistication needed for formal documentation in big international organisations. Which is not a criticism, they’re just aiming at a different market.
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I’m not telling anyone else how to run their business, but in my former work activities we would send out a snapshot that could NOT be edited directly (locked for changes with change tracking) so that the changes could be merged back into the document by an editor. Clearly different folk have different rules and procedures, but if my name is on a document, I want to know that my contribution remained as I intended, and were not randomly edited by some rando.