The 16th Amendment does not make an income tax legal.
Rather, a tax on wages is an indirect tax already permitted.
There was a supreme court case on a tax on rent on property. The court properly held that a tax on rent for a property was close enough to a tax on property to be considered a direct tax, and thus only legal if levied in proportion to population.
The 16th Amendment permitted a tax on income, from what ever source, overriding that supreme court decision.
The 16th Amendment did not override the previous Supreme Court decision.
The 16th Amendment removed the founder's wise protection against direct taxation. The 16th Amendment removed the provision to levy taxes in proportion to the population.