The argument is that 1:1 instruction, or tutoring, is a superior way to acquire knowledge. Having lots of information available is great, but not a substitute.
On this specific topic, I must admit I do believe 1:1 tutoring is overrated. I've taught myself most of what I know, and the rest I learned in a classroom. I have never had one on one tutoring. I may not be representative of the population, but I bet most people don't need near as much tutoring as a tutor would have you believe, they just need access to accurate and well organized information.
An intelligent person who is privately tutored can be performing at a college level or above when they are in their early teens. They can be at a doctoral level when they hit their twenties and then spend the entirety of their most productive years making use of their education. Compare that to our current educational track which has most people achieving their doctorate in their 30s. Performance for the average autodidact would likely be much worse.