No, it doesn’t.

Regardless of the backend stack, if you maintain both the front end and the backend, it is categorically less effort to only maintain the backend (ie. just run an API).

Half as much effort? 3/4? I don’t know, maybe your UI is a man autogenerated swagger frontend and it’s (43/50) as much effort.

It depends... but it is always less effort not maintaining an external user facing UI.

I think the counterpoint to this would be Google Search. The core product is incredibly simple from a frontend perspective, but the backend is world-class engineering.

I think making information usable is hard. This means that the burden of the development falls on whatever is making the information useful. If you simply can query an API and get stuff back that's valuable because the data is already processed, UI is pretty easy (aka Google). If your backend is returning raw data that needs to be organized and displayed, and users need to be guided through complex processes that are just simple CRUD operations server side, you have a much harder UX/UI challenge. Most things fall somewhere in the middle.

Well, what does your API actually do? If you're e.g. Heroku, your front end does almost nothing in comparison to the rest of your product. Why would running the backend of a globally distributed infrastructure-as-a-service company be easier than maintaining the front end?