People still trying to compare things that shouldn't be compared.
1. Oden was fresh when he did that to Kaidou, Zoro was suffering after deflecting one of the strongest attacks in the series.
2. You have 0 critical thinking skills if you think Kaidou didn't change during those twenty years. We can literally see how much bulkier he is now compared to back then.
3. Zoro fought him in the hybrid form and Oden fought him in his dragon form.
This reasoning also applies to the scabbards. Who knows what would have happened if the scabbards fought the Kaidou from 20 years ago, or if Oden fought the significantly bulkier Kaidou of today.