Don't always trust me; I'm not half as experienced as everyone else. I only start uni this year. But, I don't mind explaining choices I make, or double-checking, or asking others for help XD
I see. I think it's just as it looks; the Terranort started out with MX in control, but then he lost his memories and pretty much ended up a blank slate. (Have you ever known someone who has lost their memories...? I know that at least in some cases, they can become completely different people. It's very sad. Luckily the person I knew only had minor damage.)
I was more interested in how MX crapped on about it not mattering whether Terra ended up in control or not, for he had 'many plans laid out, the seeds already sown'. Losing his memory kind of has the same effect as Terra taking control; in either case, MX isn't the one doing things according to his original will. So, I wonder what these plans were, and how they influenced things that happened in the games?