Mouse only = one-handed user = slow user = no work
I trained on AutoCAD 10 for DOS. The interface was script-based. Then, as now, you could just type or paste a long series of commands into the Command Line. The few mouse-activated commands were referred to as 'shortcuts'.
When I started work I used AutoCAD 12 for Windows. Suddenly all these Icons appeared but I mostly still used the keyboard.
Then I used AutoCAD 12 LT which used a different Icon set. Keyboard still worked.
Acad 13 - different Icons
Acad 13 LT - different Icons
Acad 14 - ditto
And so on.
And then the Ribbon....
And still I use my keyboard. If I didn't, I reckon my right hand index finger would be capable of cracking hazelnuts by now.
And there's a lot less hand-eye coordination involved in using a keyboard compared to using a mouse or touch. Better for the eyes, better for the hands.