isn´t Oden´s AP implied to have been much better then Zoro´s scar?
Not exactly... They both scarred Kaido but there are 4 key differences;
1. Oden scarred a younger Kaido, Zoro scarred an older one. So fort starters, this Kaido should be stronger.
2. Oden scarred Dragon Kaido, Zoro scarred Hybrid Kaido. Which makes the version that Zoro scarred even stronger.
3. Oden was in perfect physical condition, Zoro had 30 broken bones and was pretty much at the brink of death. In One Piece, wounds have a direct impact in your overall fighting capabilities. So Zoro was actually nerfed during this feat.
4. Last but not least, after this, Zoro unlocked OCoA and ACoC. Two overwhelming new power up that made Zoro skyrocket. Luffy went from being folded in base to being able to land some very clean hits on Hybrid Kaido once he got ACoC, so the buff is significative.
Overall, I don't see how Oden's AP is better than Zoro's