I'd rather use an over engineered solution that has lots of libraries available for implementation than to build a home baked auth solution that's based off of ignorance.
Did...did you read the article at all? The author, A. Has written successful Oauth2/OpenID libraries, B. Has built businesses atop them, C. Has still seen a lot of people misuse them, and D. Is recommending libraries that are narrower in scope, not homegrown auth solutions.
The author specifically mentions being an oauth provider. What you're apparently ranting against is "why not be an oauth consumer?" Nobody has an issue with that. (And the article explicitly states "oauth consumer? This is irrelevant to you")