That's absolutely true. If the person works 20 or 30 hours a week, for instance, they will need from 20 to 30 weeks to accumulate the required hours.
Normally, after a pregnancy, a woman has her baby and takes care of it. The illness may come to light only after the person returns to work. Or they may realize only after returning to work that they have a health problem that prevents them from working.
That's something of an issue in law, in general. What can be done to change that? The decision-makers could consider the hours of work the woman has accumulated—we are usually talking about a woman—before her maternity leave began and decide that she needs 600 hours. That's one way to proceed. They could perhaps calculate the average hours worked over three years. That's another way to proceed. If the woman returns to work and stops receiving benefits between parental leave and sick leave, they may also say that this was in response to her employment insurance claim. There are ways to insert a sickness benefit claim after the return to work, if someone really wants to do that.