I think you're picking and choosing responses without reading the full context.That would be what a per se violation is. As example, price-fixing is illegal regardless. Apple was found guilty of price-fixing in the eBook case although it had a very small share of the market compared to Amazon.
That's correct and exactly the point of the rule of reason: you can even be a monopoly as long as you don't unreasonably restrain trade.
I'm responding to the phrase "but now at their current size.". Your post is very off topic.