Our concept of "computer" was not the same 75 years ago. There was no silicon, nor semiconductors. But the E6-B performs complex calculations. It is truly a computer for flight planning, because it does compute!
Nowadays we are so used to complex software and ubiquitous connectivy that we forget that basic tools such as the E6-B can be lifesavers in some situations.
My flight instructors made me use the E6-B for all the flight planning during my training, and they always pointed out that internet is not available everywhere and batteries die. But the E6-B is always there to help.