You and OP are both conflating GUIs with mouse control. GUIs are great, sure, but aren't necessarily mouse-driven. I'm not using the mouse most of the time in my GUIs.
(also are you suggesting becoming a e-sports tier performer to be... fast in executing actions on your computer? Think about how absurd it sounds. Mouse clicking on UI elements requires visual feedback and a lot more conscious effort where keyboard is just muscle memory and is vastly simpler for most discrete actions, except for a few scenarios, while being blazingly fast. Yes I'm more than aware what aim trainers are, and high-end mice are not more special than high-end keyboards. Aim trainers have completely different constraints and requirements than UIs.)