I think that is a bit of a harsh criticism of ancestry.
A person can certainly use the ancestry databases to get a good head start on their family history. There are US and Canada censuses back to 1850 that are an essential part of a person's research. Ancestry has birth, marriage, and death records of many states on-line now. WWI Draft Registrations is an excellent database. It has excellent Civil War Records summarizing the war record of an individual in the Civil War and (usually) a link to the history of battles of the unit the person was in, and a record of whether they survived the war or not.
Sure, it is missing a lot. It has limited records before 1850, virtually no wills and probate records, limited cemetery records, no real estate records, etc. But, I am pleasantly surprised as each year goes by to go back to somebody and see records added by ancestry in the past year for that person.
So, it is not the complete answer to everything a person needs to have; but is a good place to start.