Also the serums used on the Titan transformation were modified right? Is it possible that there's a difference between Ymir's accidental absorption after being a Titan for so long is different from the intentional one when she was eaten? I don't know since we never saw what happened, but it seems plausible?
Wasn't there a comment in the Reiner flashback episode that their batch of Warriors was much stronger than previous ones?
Could be something to it.