And Lea didn't change as much either, so I guess it also can't be the experiments, eh?
Plus, if it were the experiments, that would make Lea and Isa as the first Nobodies to have been, not the very last ones as their ranking suggests...
Or maybe that's the point. Perhaps they didn't lose their hearts in a year.
They were experiments. Why would you rank them higher? If you created them, you make yourself above them. The rank is in order of joining, not so much creation because they had to hunt the other members down. We don't really know how long they had been around as Nobodies. Except for Roxas.