Well, given that I am typing this about 15' from an IBM POWER S914 running the i operating system, I'm not sure its lost. Our accountants hate GUI stuff and love the green screen. Its amazing to have what essentially is a low maintenance machine that calls IBM when something isn't correct. We have the last i Series (a pre-POWER model) that lasted for over a decade, and I do expect this one to make it the same amount of time. It is a bit obtuse, but I dearly wish some other OSes would examine themselves for self administration to the level of the IBM i Series.
As late as 2011, we had a custom payroll system on MS-DOS. I was always blown away by the speed it's users achieved. They really flew through the menus and knew all hotkeys and commands of the TUI by heart. When they got "upgraded" to a modern GUI based system, it really slowed them down. Of course learning a new thing always takes time, but that's not the whole story. Especially with ever-changing websites that usually don't care about hotkeys, the mental load of visually scanning for elements and clicking them with the mouse can be really slow. And it always fascinates me how it was perfectly normal and expected for mere users to use a TUI while today I've heard grunts even from junior devs and self-proclaimed power-users when I told them to use the CLI for this or that.
How times have changed.
IBM i is fascinating, and in a world of ever-changing tech-stacks I sometimes yearn for a stable environment where you don't have to fight with 10,000 node.js dependencies every other month just to keep that payroll website going. I've never came in contact with IBM i or POWER tech in a professional capacity, but have purchased an RS/6000 and, more recently, a TalosII system to play around with ppc64le :)
The biggest key with the "green screen" terminals is they would NEVER EVER lose a keypress and they would buffer them, too.
So even if the computer was actually quite slow, if you knew what you were doing you could "type ahead" a few screens into the system, and then wander off and do something else.
That just doesn't work on GUIs (some rarely are well designed so that it can) and certainly has zero chance of working on webpages.
I honestly wish someone had come up with some text markup language and "browser" so enterprise developers could deploy text UI apps. The web is just awful for the back office people. Frankly, I wonder how much money is being spent on the web when a TUI would have been more productive.