I think that the accelerator vibrations is not bad, but I really really feel the brake pedal vibrations are too light.
They are technically both the same motors...
The issue is not the strength of the motor but the method of attachment. Fanatec have chosen to use a spring clip to mount the motor. These are ineffective at transferring vibration - as they are flexible. Spring clips also lose clamping force over time, and often have inconsistent clamping force from the get go - seems like one of yours is weaker than the other. You could try shifting the motor in the clamp or tightening the clamp but it's a design problem.
Would there be enough power to add a second motor for both the gas and brake?