What was the result of that fight?
Lancelot in full working condition.
Guren's arm broken, meaning it's useless in a fight.
Even if you want to say that the cliff broke the Gurren while the Lancelot didn't(which is asinine, as the gun has the power to disintegrate steal beams, which is a magnitude or eight greater than a fall of a cliff could ever do) the fact remains that position in a fight is just as important as weapons, and no less a telling of the skill of the soldier. It was either Kallen's stupidity or Suzaku's cunning which forced her at the end of the cliff.
You Kallen fanboys are ridiculous. She was never meant to be anywhere near the level of Suzaku, and has never proven herself such. Ask /m/, they'll tell you.