The whole problem is mapping privilege to users and groups, so doas doesn't solve the issues explained in the article.
> The key difference here would be that www-deployment can not delegate as easily to arbitrary users, as they would need to ask someone with root access to add additional users to the www-deployment group. But I am left wondering if this use case (if it is important enough)...
Delegation is the killer feature of the object capability model. It's not just important enough, it's the most important. Keep in mind that the ACL model allows delegation, too, it's just unsafe. Users share credentials all the time. Capabilities allow delegation in a way that can be attenuated, revoked, and audited.