The only open source mentioned in the post is their encryption. Not the document editing software. OP please remove your change to the article title, it's extremely misleading.
I like how there seems to be more and more alternatives to MS Office, even from big companies like Google. Best case scenario, this could lead to companies actually starting to use an open format, like ODF, so that all these different office applications can be used without causing issues in the file and that would pave the way for open source alternatives, like LibreOffice or OnlyOffice, to become viable alternatives for a lot more people and companies. Do Google Docs and Proton Drive use/support ODF? I'm pretty sure MS Office supports it.
They're just too expensive. Like, sure, it costs money to run, but 3.49€/month (the discounted 24 month rate) for the mail only plan, 15 GB storage. (41.88€, $45.17 USD, $67.28 AUD per year)
That's really expensive if you just want mail.
The other stuff, is also really expensive. To the point that makes you think, "there is no way google is making THIS much to make up the difference in advertising to me for a comparable plan".
Interesting.
I will try to find out if it's 1:1 in handling .docx like OnlyOffice which i hope it is. It sucks that OnlyOffice won't run natively on Wayland.