I am surprised that lack of control and customizability over the frontend is being billed as a feature.

I've built multiple internal tools like those in the example section, and even with a solid framework like react-admin, one of the first requests you're going to get from internal stakeholders is tweaks to the UI.

It's a myth that internal users aren't as demanding as external stakeholders. If anything, they can be more pushy.

I would not want to launch an internal tool, except as an engineering-only POC, unless customizing the frontend were at least as easy as customizing the backend.