The purpose of the census was never to gather information to be used by future genealogists. That was just an accidental benefit.
The original purpose of the census was to determine the free population of each state, excluding slaves and Native American Indians, and the slave population, in order to calculate the sum of "the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons" for purposes of apportioning seats in the House of Representatives and a hypothetical direct tax that the states would have paid to the federal government.
The purpose of the census has always been to gather statistical information, not to gather personally identifiable information. Originally, they recorded the name of only the head of the household (usually the husband) and the number of slaves, children, wives, etc., but not their names.
The information useful to genealogists was added for a variety of reasons, but genealogy was never one of them. The lack of questions that would be useful for purposes other than those for which the census is conducted in no way relates to whether the census is meaningless or still fulfills the government's purpose in conducting it -- even if not the unintended purposes for which genealogists use it.