It is not possible to rely solely on rote memorization, and to get a PhD is supposed to require making a substantive original contribution to a field.

Having said that, the skills required to get a PhD are pretty specialised - it's absolutely not a given that people with PhDs are highly-functioning human beings, or even necessarily capable of holding down a conventional job. They will at a minimum have demonstrated the ability to self-organise, a high level of bloody-mindedness, and some very deep knowledge in a probably very obscure field. But unless you move straight into solo academic research in the same field, that's not the same thing as being trained in any strong sense.