The booster doesn’t use tbe grid fins except for re-entry and landing.
The grid fins help slow it down from high suborbital speeds and at high angles of attack. This prevents them from needing as much fuel to slow down before landing. Grid fins also require smaller actuators, saving weight. The other benefit is accuracy. The grid fins provide very high precision for ordnance such as the MOAB or R-77, and likewise allow SpaceX to land the booster on a boat in the water.
The use of the fin as an airbrake and to slow the rocket down demanded different grid shape than what is seen on the R-77 which benefits much in the same way - but optimized the grid for low drag rather than higher drag.
In response to a question about the future of American spaceflight, Elon Musk said that Boeing and Lockheed have relied too much on the Russian RD-180 engine.
First of all, you moved the goal post from Russian rockets to Russian engines, proved wrong on both and now you’re saying we use Russian stuff in general at an even lower level… We were talking about SpaceX. They don’t use Russian equipment. They designed their own.