Paul Swail has spoken a lot about this and has an upcoming book around the concept: https://serverlesstestinghandbook.com/
For one, the article assumes the tools you use to replicate your production environment locally aren't accurate; with localstack, they are accurate. It's seamless, truly. I recommend you give it a try instead of spending the extra cash to have your developers deploy into the cloud constantly.
Another thing to note is that this seems only true for a specific architecture, if you're writing serverless functions. Not everyone is or should be doing that, so I'm not sure "you should always test in the cloud" applies as a "context free" rule.
Finally, it sounds like the author had a lot of trouble getting his local environment to work. Maybe folks who have a bit more experience working with the technologies involved in their services don't have that problem, and it's a little arrogant to assume that, just because you had a problem, that it's a problem for everyone else, too.
Overall, I just don't think commenting, "This service nice, but using it is an anti-pattern" was quite as productive of a comment, in general, as you meant it to be.