I'm trying to imagine how Google Docs could be worse than Microsoft Word stored in your One Drive, or Microsoft Word Online. Both services don't access your private word document unless required by law enforcement.
1) Android keeps a log of everywhere I've been. It randomly turns on Google Assistant and records my voice. There is a ton of telemetrics going to Google, and no way to know what it is.
2) Google Docs literally keeps a keystroke-by-keystroke log of everything I've ever typed into Google Docs. If you typed the n-word and erased it 3 seconds later, that's in your permanent record.
3) Google lies about what data it collects and stores. Your Google Export won't include things like #2. That's a violation of GDPR.
As a footnote, #3 came up when I had my GSuite account attacked by an insider. I couldn't do forensics without a security up-sell. I wanted to know what IPs had accessed my accounts, at what times, and what they did. That kind of auditability once one tier up -- if I switched away from the (at the time free) tier, permanently.