Why the chauffeur? Can you not afford a valet?
Of course it's optional. You may get asked what was wrong, but you are well within your rights to demand it be removed for whatever reason. They can't force you to pay it.
Michelin service is very good compared even to the likes of Orwells or Inver.
The service does have to be consistently good, but because what is considered 'good' is so subjective, the standard varies according to what the customer requires. If all you want is to be waited upon by servants, then that's what you get. If you want a warm welcome, with staff who are happy to chat with you, they'll do that. If you want ketchup with your thrice-fried pommes confit, that's what they will provide. If you want to feel lke royalty, that's what they'll do. If the guest asks for a substitution, they should not be told that this cannot be done - NOTHING within reason is impossible.
Staff need a tremendous depth of knowledge about the restaurant, the wine and food and how it's prepared (almost the same level as the chef), the etiquette, and everything else that goes with it. That takes a lot of training and study. This isn't just a normal waitering job - It's a full-on profession at this level.
But if you just want one all-inclusive charge, drop the 10% service charge and add 20-30% to your base bill. That still won't fully cover the 'proper wage' level, but it should help illustrate the sort of value these places attach to their service staff.