From Shinkansen platforms on the far Yaesu side of Tokyo station to the 4th underground level for Narita Express on the Marunoichi side is indeed a long way and you go through the entire corridors from one side to the other.
Originally, when Narita Airport rail link was proposed, there was to be a Shinkansen line straight to Tokyo station, but when that plan was abandoned, the existing Narita line was extended to the airport and was connected to the new Keiyo line which uses the newly-excavated underground levels on the other side of the station. I have seen many foreign travellers struggling with heavy luggage transiting Tokyo station during day-long rush hours, on escalators, corridors, elevators and stairs.