" the idea being that if Amazon bought every retailer in the whole nation but prices didn’t rise, then it would be okay"

How could anyone possibly agree with that statement?  This would limit consumer choice as well as establish a monopoly on employment.

The EU has done the right thing. Anti-trust legislation was pioneered in the United States for very good reason -- monopolies help no one but the plutocrats who control them.

It is a pity that Canada and the US are not more aggressive with this kind of legal action.  Competition is what drives innovation, consumer choice, and fair prices.