[invalidator]

You don't pull all of the control rods at the same time. You can fully withdraw some number of them, then control the reaction with a few more rods.

There are several strategies to provide additional control so it's not all at the bottom. For instance, in a PWR, reactivity decreases with temperature, so additional coolant can be injected where additional reactivity is needed. In the RBMK, a small number of rods were inserted from the bottom to provide more axial control.