It isn't outdated, it is an economics definition of a monopoly, and isn't even that: a monopoly is perfectly fine, AS LONG AS the economic power isn't abused to prevent competition which harms consumers.
What the author is proposing is that regulation is no longer based on economics and economic power, but on a vague definition of monopoly, and people are absurdly trigger-happy when calling something a monopoly.
The reason why anti-trust is based on precise economic definitions is that it leaves as little room as possible for the government to favor friendly players. When you need to prove harm to consumers, the bar is high, as it should be.
Otherwise, any government in power will simply abuse their own monopoly on regulation to favor and transfer wealth from society to friends.
The classic example is: Coca-Cola has a 95% market share of the cola market in some countries. Does it mean it has a monopoly? No.
If it had 100% of the cola market, would it have a monopoly? No.
Because the cola market doesn't exist in isolation. Colas compete with all other sodas, with water, juices, etc. for a share of wallet and a share of stomach.