The best thing about all character-based applications I've ever used is the keyboard buffer. Even if you're using a TUI on a system that has a slow backend, it almost always blocked the thread and didn't consume from the buffer during waits, so if you knew the sequence of keys was "Total, F1, 1, Enter, Enter, Tab, 2125551234, F10, 1, Enter" you could just enter all those keystrokes as fast as you could and the system would eventually catch up with you, meanwhile you were bagging a purchase or counting out the cash, whatever.

The GUI also has lag - especially in the era of web-technologies-bloat, more lag than ever - but whether touchscreen or mouse there can't be a buffer, so each lag requires you to stare waiting for the next UI to be drawn.