You could still do this in the GUIs of 25 years ago, you'd just memorize the keyboard shortcuts and use them. They'd buffer so you could type a series of operations faster than the screen could render them, and basically every function was accessible from the keyboard. But the GUI had the advantage of discoverability - if you didn't know the keyboard shortcut, you could just work your way through the menus and find it.
While possible, the uptake/usage is very low once it requires lots of CTRL / ALT / CMD button sequences. Take something like Excel, which many users use daily for work, but most people likely only use less than a dozen common keyboard shortcuts. Practically nobody navigates the ribbon with their keyboard.
I'm in a role of Finance / Excel "super user" in my profession. There's a subculture of keyboard shortcut enthusiasts, but generally everyone is using their mouse a lot. I myself have about 20 that I use and rarely incorporate a new one into the mix, it has to be an action I perform repetitively for me to care enough to memorize seek out and learn the shortcut. I find navigating the ribbon usually requires too many keypresses and I instead have a custom quick access bar that I put everything I want access to so I don't have to toggle differing ribbons, I still use my mouse even though I know I could use my keyboard. It doesn't feel easier
But it’s true that the menu systems often made the accelerations and afterthought, and regularly used functions for some people had no shortcuts and no way to set them.
I still think a World of Warcraft style action bar, user configurable and multilayered, would work just fine for power users. You can put anything you want in position eight but most people have the same things set for 1-5.
