Edward's final exchange with Sakazuki is hardly what one might accurately call a "rape". For starters, Edward got a free-shot at the back of Sakazuki's head (which is a significant advantage, considering the fire-power Edward possessed), and furthermore, Akainu took off half of Edward's head with his swift retaliation in their brief struggle. Besides, it's questionable if Sakazuki was even knocked unconscious (though he undeniably was defeated), as he is seen grunting and cursing Edward as he falls down the schism. But even if he was, he recovered his senses quick enough to save himself and start burrowing through the ground, with a speed that surpassed Jinbe's sprint for the bay (who began dashing before Sakazuki was grounded by Edward).
For a comparision, say that Mihawk had another brief battle with Vista, where he eloquently knocks out the flower-man with a beuatiful riposte, but before Vista's lights went out, he manages to retaliate and split Mihawk's head clean in two. Would you then say that Mihawk stomped Vista?
Yes, Edward was gravely wounded, yet spurred by love for his lost son and (wordless) rage towards the man who had just killed Ace before his eyes as he was, I think his injuries hampered him less than you think. We have many examples of Luffy (as well as the rest of the Straw-Hats) going full throttle, pushing his body far beyond it's limits with sheer willpower, despite horrendous wounds and mounting exhaustion (e.g. against Crocodile and Lucci), and I think Edward's victory over Sakazuki should be taken as a sign of Edward's truly herclean endurance and unyielding power of will - and not as an indication that Sakazuki has nothing on the "real" top dogs after all.