And I don't mean the speed of light kind.
At 14 stories tall and traveling upwards of 1300 m/s (nearly 1 mi/s), stabilizing the Falcon 9 first stage for reentry is like trying to balance a rubber broomstick on your hand in the middle of a wind storm.
EXACTLY the same as takeoff. NO difference.
Same amount of fuel? No, so not the same moments of inertia. During launch the engine is pushing in the direction of travel, during re-entry no. During launch, the aerodynamics include that nice fairing on the nose, which should be a bit less chaotic than coming engine first down. The period of 1300 m/s travel that you quote and compare to launch is not during launch (0 m/s) - it is probably closer to the period of maximum dynamic load and clearly during super sonic travel. The reverse part of that travel, the period of maximal dynamic load during re-entry in a non-aerodynamic configuration is rather more difficult than getting off the pad.