Word is just a bloated wordpad, and that's how people use it - to write text with paragraphs and justifications (recently wordpad supports docx). Excel is just a bloated csv viewer, that's how people use it - to make tables with text in them, notably price lists. My company is an ms shop and uses ms office offline and google docs for collaboration. First time I hear that ms office can into collaboration beyond sharepoint.
Then you have a limited view of creative way how humans collaborate, and clearly don't need bloated Office at all.
It's network effect. People use ms office not because they need its features, but because they receive ms office documents.
We converted some our docs from docx to markdown. The twist is that markdown supports tables, so it can replace both Word and Excel. Then I guess gitlab renders it. Literally markdown. It's stored in git, supports diffs, version history, collaboration is done with merge requests.