The problems with ratification of the 16th Amendment are well known, although I think this guy overplays them. Some of them are quite technical - for instance, the signatures required for a state to verify ratification may vary from federal requirements. Even good constitutional attorneys may vary on which is the correct requirement. One thing with which everyone should agree though is that the ratification (or lack thereof) of the 16th Amendment is of only academic interest. As a point of law, the 16th Amendment is established.
Venix's position is amusing, much like Butthead saying "Don't be stupid, Beavis, there's always been TV!" In fact SCOTUS ruled that not only were direct taxes prohibited except via apportionment, but indirect taxes which approached the function of direct taxes were also prohibited. (No capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or Enumeration herein before directed to be taken.) Otherwise there would have been no need for an Amendment establishing Congress's right to levy direct taxes. It is very clear that the Founders' intent was that the federal government would fund itself through duties and other indirect taxes. However at the time the solvency of the federal government was in question and as Hayabusa Rider says, government's first and highest obligation will always be to itself. Thus we have the 16th Amendment.