I don't know what the formal definitions of any of these things are, but I assume (hope?) that it's important not to equate being successful with being a monopoly by definition. If Ford came out with an amazing new car tomorrow, and suddenly 95% of new cars purchased were Fords, we probably shouldn't initiate trust-busting action against Ford on that basis alone. We want car companies to try to capture market share by making better cars.
I don't know exactly how we contend with this definitional problem, but intuitively I think it should have something to do with prices and behavior. For example, if we were a fly on the wall in a Google exec meeting, we might be curious about whether they're jacking up the price of ads because they know no one can compete with them, or whether they're sensitive to charging more than their smaller competitors do. If they're behaving like their competitors are a serious threat, then intuitively they're probably not a monopoly, and it probably doesn't make sense to trust-bust them.
But anyway I'm not a lawyer, and I don't know what the current thinking is about any of this stuff.
I don't know exactly how we contend with this definitional problem, but intuitively I think it should have something to do with prices and behavior. For example, if we were a fly on the wall in a Google exec meeting, we might be curious about whether they're jacking up the price of ads because they know no one can compete with them, or whether they're sensitive to charging more than their smaller competitors do. If they're behaving like their competitors are a serious threat, then intuitively they're probably not a monopoly, and it probably doesn't make sense to trust-bust them.
But anyway I'm not a lawyer, and I don't know what the current thinking is about any of this stuff.