Linux

I think you and I are using two different definitions of the word "powerful", or are at least applying them to subtly different aspects of the discussion.

1. I don't know if you are familiar with basic finite automata theory, but a Finite State Machine is provably less "powerful" than a Turing Machine. This is the definition of "power" that I'm using, "power" as in "expressiveness". i.e. The fact that you can literally create a terminal as a sub-element within a GUI if you wanted means that a GUI is provably more "powerful" (or more expressive) than a TUI. And thus the best GUI for a tool will always be better than the best TUI for the same tool. (Comparing the worst GUI vs the best TUI is a waste of time).

2. But you're using the definition of "powerful" as in a "powerful programming language". This is a common use of the term, but is much more fuzzy and harder to quantify. It's no longer synonymous with "expressiveness". Generally a language is "powerful" if you can get "a lot done" with relatively few characters or operations. Ex. Python is often considered more "powerful" than C because you can do in a single line what would take dozens or hundreds of lines in C. Similarly, you're saying that a developer can make a comprehensive TUI using less time and effort than it would take for them to make a GUI that's at least as good (including integration with other tools afforded by pipes and redirects).

And I agree with you. But hopefully you also agree with me that a GUI is objectively more "expressive" than a TUI, and in that sense has a higher ceiling for how useful it can be to a user.