That's just the sign of a bad assistant, not a problem with the role itself. Competent assistants have full knowledge of their boss's schedule and will make the appointment without their involvement.
Sure, they have access to the schedule, but seldom does someone want their calendar being filled up and someone else deciding what their priorities are.
So it ends up being more about having a status symbol.
A good relationship includes a huge amount of trust, including that your assistant understands your priorities and can do some decisions autonomously. That's what you get from paying a full-time assistant instead of a simple AI.
So it ends up being more about having a status symbol.