Something I haven't seen mentioned much on this thread is that the ~top feature people want from SDKs at this point is good static types – so you can get autocomplete, docs-on-hover, etc in your editor. Way better than switching back and forth to the docs and crossing your fingers.
Doing that well means copying every little change into the SDKs (forget about it) or using a generator.
The open-source codegen tools (ie, https://openapi-generator.tech/) are pretty crappy, so you need to either build the SDK yourself fully, or spend a bunch of time wrestling with the generator get it halfway-decent, and then you're still letting your customers/developers down.
Disclaimer, I'm starting a company to make it easy for anyone to ship a great SDK with their REST API: https://stainlessapi.com