Families investing under the name of the zero income/lower income person is a feature, not "exploiting a loophole".
Australia is one of the small number of countries that does not allow families to pool income and assets for tax purposes. (It does pool income and assets for income and asset tests for claiming government welfare though - funny, that 😉)
This means that of you have 2 families (say 2 parents and 2 kids), both families have the same income of $160,000, but in one family this is earned by 1 parent and in the other family both parents earn $80,000) the former family pays FAR more tax than the second family despite having exactly the same gross income.
Instead of fixing this and aligning more with what other countries do, the 30% minimum is a move even more extreme in the other direction.