In Blank Points, when Terra and Master Xehanort's Hearts are talking to each other inside Apprentice-Xehanort, MX discovers that Terra also has Eraqus' Heart inside of him as well in order to give Terra a 2-on-1 advantage to help him resist. But then in Dream Drop Distance, it is revealed that MX eventually gained full control of the Apprentice anyway! Shouldn't Terra and Eraqus' Hearts have had greater influence over AX since they outnumber MX's Heart? And what was the point of giving Terra this "last laugh" if he was just going to fail later anyway?

I think maybe it's perhaps "Quality over Quantity".

^my guess is what he said

well its MX vs Terra that we are talking about, so...

"Darkness rules your heart. It gives me control. Muscle and sinew that once obeyed you now rebels against you. How you can remain here at all confounds the mind."

Perhaps Terras anger of his situation helped MX take control from AX