Some really don't have a clue.
I NEVER asked if a guest wanted change. It is presumptuous and rude.
I always brought it and let them leave it.
But yes, essentially, you are paying the server for the service, and the restaurant for the food, AND for the taxes on the tips you paid the server. (which the server has to pay, even if you didn't tip!)
If you only paid the restaurant, in order to keep that level of service, most establishment would have to raise prices at LEAST 30% if not 50%. Some maybe might have to even double their prices. Remember, it isn't just the wages that would cost more, they also have to pay unemployment, SS and Medicare taxes on those wages paid. Less wages paid, means less payroll taxes.
And now with "Affordable Healthcare?".... don't get me started.