No, this assumes that there are not many women (or men for that matter) whose hyper-productivity can make up for a 2-3 year leave of absence.

Not quite, because not every woman will vanish from work for 2-3 years.

Such laws make an employer indifferent between a man of quality Q and a woman of quality Q + P(taking leave) x (cost of leave). Whether or not hyper-productivity is required depends strongly on P(taking leave) and the cost of leave.

One other thing to note is that a lot of businesses are now granting paternity leave equal or near so to maternity leave.