I meant if there was some external force like a wind shear or grid fin/hydraulic line failure that pushes the rocket hard enough on descent to alter it's vertical orientation, those grid fins won't really do much to correct that force.

> Gravity and wind will do the job for you

You cannot control gravity or wind. You just have systems that manipulate those forces. Grid fins are a passive system in that they manipulate the fluid the rocket is in to steer it on course but not to correct drastic attitude alterations.

But again, if the updates to the hydraulic lines work out, then they won't need the active thruster system. Adding an active thruster system is just engineering for worst case scenarios.