There's noting needing a rebuttal. Smith wasn't saying that's the ideal form of government. He was saying that's a corrupt form of government.
I'll also point out, as to the question being asked or if that was some 'central point' - according to taxation rules Smith actually did lay out, plenty of rich people would be due a tax cut, and plenty at the bottom would be paying a lot more taxes, if going by Smith's guidelines about what is a 'fair share'.
Those arguing about that age old 'fair share' are foolish to use Smith as a source, if socking it to the rich is their goal. Smith didn't even like income taxes.
He was talking about civil government as it exists when created for the purposes of the defense of property, which basically all modern governments are. It doesn't matter if he had an idealized government that was different, it was his evaluation of governments with similar aims to ours. It's not really foolish to talk about him in relation to taxation either, as he was clearly in favor of progressive taxation, just based on different criteria.
It's also kind of an obvious statement. I mean the protection of personal property is quite clearly one of the primary aims of our government. Who cares about that? The people with the most property. All that aside Smith could not possibly have imagined the sort of society we live in today, so saying what he thought would be the appropriate burden today is kind of a waste of time.