It is not the display name that has to be unique, it's the handle. We have the same issue with email, you get a "name" and an "email address". If the name reads "Bill Gates" but the email address reads [email protected] then you know it's problematic.
Is it trivial for the new user? Probably not. That is why organizations have training courses, where they tell the employees: Pay attention to the important parts (aka the handle, not the name)
Is it trivial for the new user? Probably not. That is why organizations have training courses, where they tell the employees: Pay attention to the important parts (aka the handle, not the name)