A monopoly doesn't mean users don't have choice! Like the car manufacturing example, there are economies of scale that let Google build up external barriers and dictate anti-competitive behavior because of the dominance in the market. It isn't about user choice, it's more about website owner choice.

To play off the merged car company metaphor, imagine if 80% of all cars were Ford. And Ford comes out with an electric car that is really efficient (AMP), but it really only gets that added boost if every gas station in America install a special Ford Pump that charges cars in 2 seconds. And the gas station doesn't get any money from the pumps, but since 90% of cars are Ford they better install those pumps if they want to sell chips and soda in their little store. Otherwise, everyone will just use the gas station across the street.

But hey, no one is making them install those Ford Pumps! And it's great for Ford owners... until all the gas stations start to close.

AMP is bad enough, but having it influence pagerank means Google is leading websites to accept AMP or immediately lose Google traffic. And because Google is dominant in providing traffic to sites, there is very little choice here for site owners and no benefit.

I think where we disagree is "do nearly the same thing". If Google search results are qualitatively better than those of their competitors, to the point it's a different product, it's a monopoly. You are free to disagree on that, but that doesn't make my argument a straw man.