Nothing to do with physics.
I’m sure you’re aware, you can change the frame rate of your game with t.maxfps, I think the command is.
Try removing the world delta seconds and setting the fps down to 20. That’s what your game will play like on a heavily loaded machine. You discover that everything moves really slowly. Which it shouldn’t 
The GWDS compensates for that.
As the frame time gets longer, you will end up moving further, with this equation.