Marco has great defense with no offense, this was clearly shown when it took both Vista and Marco to even harm Akainu and even still it did minor damage. And this was right after there comrade was fisted through the chest, there willpower should have been stronger than ever.
We saw Marco kick Kizaru and it did no damage, he kicked Kuzan never seemed to harm him either. His capabilities during the war were consistent as in, he can't hurt any of the admirals but because of his fruits ability to regenerate from any damage no matter who inflicts it he will always heal. That is what makes him a difficult opponent.
