I wonder if GPS has downplayed the role of having to memorize the streets of London.

Good question. It has not changed because of that. Drivers are supposed to be able to immediately choose routes without consulting any kind of map.

I would think that the experienced human driver will outperform GPS when it comes to selecting optimal routes and alternates at various times of day, dependent on moment-by-moment assessment of traffic conditions. That's just a gut feeling, no cite to back it up.