I'd be interested in some concrete examples of things GCP have depreciated. I'm an (admittedly fairly light) user of GCP and haven't come across any myself.
I saw that he mentioned a few of them in the article. He writes: I can tell you that virtually everything I’ve used, from networking (legacy to VPC) to storage (Cloud SQL v1 to v2) to Firebase (now Firestore with a totally different API) to App Engine (don’t even get me started) to Cloud Endpoints to... I dunno, _everything_, has forced me to rewrite it all after at most 2–3 years.
Personally, I think most of them seem quite sensible. Having a 'support everything forever' approach is obviously going to impose a huge burden on the teams who maintain this stuff which is then going to limit the ability to make anything better. The depreciation notices generally seem pretty good (12-15 months notice by the looks of it, sometimes followed by degraded functionality rather than complete removal of the feature).