There's a huge array of additional differences between the productivity apps in Office 365, compared to Google Apps for Business. Office documents almost always survive a round-trip through the Office Web Apps. For example, you can use Word Web App to open a fairly complex Word document, make a few changes, save it, and expect to get back a document that looks more or less like the original. You can't add any fancy formatting to the document in Word Web App — the options aren't there — but at least you won't break anything ... usually.
Google Docs, on the other hand, has no such guarantee. In my experiments, I've found that most simple documents go through the round-trip with few problems. Save a straightforward memo with Google Docs (File, Download As, Microsoft Word), and you're likely to come up with a reasonable rendition in the DOCX file. Not long ago, Google Docs broke a very large percentage of all the Word documents handed to it. Now, it appears to me as if Google refuses to open Word documents it doesn't understand. That's an improvement, albeit a frustrating one.
That said, Google Docs, Sheets, and Slides have nary a fraction of the features offered in the desktop versions of Word, Excel, and PowerPoint. You would never want to put together a moderately complex document in Google Docs, for example. Just getting the headers and footers to work right would drive you nuts. Then again, complicated headers and footers in Word aren't a walk in the park, either.
The Office programs are well established and mature. Google Apps are scrappy and improving. Case in point: pivot tables. While the Google implementation of pivot tables in Sheets isn't as capable (or complicated) as Microsoft's, Google hits the high points very nicely.
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