The article misses a really important point that you can't just revamp the UX for a product used by billions of users without some pretty serious blowback. Startups like Notion have a great deal of flexibility to tweak and innovate on their UX as much as they like, but even changing something minor in Gmail or Google Docs impacts orders of magnitude more people, using the product in such a huge number of environments -- phones, tablets, PCs -- in every language and every corner of the world. Every time Google has tried to make a major UX change -- look at Inbox, for example -- the challenges of bringing all of the existing users over to the new experience are very real. As a result, the UX tends to evolve in smaller steps, which (of course) results in the final result being more of a hodgepodge than you would get if you just started from scratch.
Google has very good UX designers, UX researchers, product managers, and engineers. These people know how to design good user experiences and care very much about the end result. But there is the reality of being boxed into design decisions that are difficult to undo without making some really major changes that are highly disruptive. Now, you could just say that Google should bite the bullet and hit reboot on some of its bad UX decisions from years ago. That is always an option, but it is often difficult to justify the benefits of an improved UX versus the productivity hit to all of the existing users.