#1 This is 2020 and everybody's collaborating on a single doc with comments. But how do you point someone to a comment with a link? In Office 365, you can't.
#2 Until recently office 365 didn't even have a grammar checker / proofing assistant.
#3 You've worked on a document and intend to quickly send a pdf over to an email? You download the file, convert to pdf and email it. Even a simple "Send this file as an email attachment" isn't available in their editors.
#4 Talking about file-format compatibility, like someone else has pointed out there's no guarantee that documents created in the online version is compatible with their desktop editors. Too bad.
#5 In version history, how can you compare two versions of the same file? Well, you can't.
Remember for Google and Zoho, cloud based document editors was their target, right from idea to finished product. For Microsoft, it was an afterthought. And it shows.