> Sure, but that doesn't really help for user-facing services where people expect to either type a domain name in their browser or click on a search result, and end up on your website every time.

It does help. For example, at my company we have two public endpoints:

company-staging.com company.com

We roll out changes to company-staging.com first and have smoke tests which hit that endpoint. If the smoketests fail we stop the rollout to company.com.

Users hit company.com

That doesn’t help with rolling out updates to the DNS for company.com which is the point here. It’s always DNS because your pre-production smoke tests can’t test your production DNS configuration.