Another way to think of it is, per percentage unit of productive capacity, a unit can move fewer tiles. With some nice management, you can easily add a unit per turn into a city on quick speed. You're not punching through a competent player doing that.
Normal Speed and nerfed whipping makes it much more difficult to defend an attack, as you've seen in PB8.
Normal Speed and nerfed whipping makes it much more difficult to defend an attack, as you've seen in PB8.