The 16th Amendment created an exception to the rule of apportionment on direct taxes, declaring that Congress could levy a tax on income from whatever source. The apportionment rule continues to be applied on all other forms of direct taxation. There are, currently, no other Federal direct taxes other than on income. All other current Federal taxes are excise taxes on import and consumption.
Additionally, the 16th Amendment was never intended to change the intentions for which the rule of apportionment was tied to both representation and any general tax laid among the states!
The 16th Amendment merely confirmed what was stated in the Flint Case, that Congress could lay and collect taxes calculated from profits, and gains without having to apportion the tax.
JWK