I worked at a big-box retailer before figuring out a career. They had an old-school TUI that was incredibly fast and well designed. Function keys to do all kinds of lookups and adjustments, advanced menus when you needed them, overall just a well designed system. People took a week or so to get the hang of it but then the skill ceiling was insane, people could get fast.

A few months before I left they switched to a "modern" GUI. It was shockingly bad. The speed of every transaction lowered. Even with optimal use it just took longer. So much time wasted.