My thought is that such interfaces are bad for learning software and for get a good overview. But when you're a power user of a certain system (like the data entry staff) there's nothing that's better.

Probably correct. And given that you're spending a comparatively small amount of time in that learning phase, would you want it any other way?

I would prefer software that I use often to be hard to learn but easy to use. Seldom used software should instead be easy to learn, hard to use. I find that most software today is in the latter category.

The reality is the world has moved completely away from terminal. The speed and productivity advantages are well known, but no one cares. By no one, i mean sales and procurement who hold cobol/green screen apps in very low regard. In other words, it's very difficult to sell trerminal applications when the competition is browser based i.e. insurance claim processing

Sell them what they demand with a browser-based presentation, then package the terminal-based presentation as a separate, paid add-on option for high-volume customers. Market the add-on as meant only for high-end customers who will take the time to train staff in the kind of high-speed entry that only the terminal-based presentation can keep up with. Sprinkle in some stats about some multiplier of efficiency and accuracy improvement, then let the customers implement what they prefer.

Between advances in ML-based OCR and dictation, I anticipate future data entry to get much more sophisticated, and demand extremely low-latency, quick-updating screens that might bring about more awareness of terminal-based interfaces in some situations.