Why cancel your preorder? If you are the type of person to only play one job, then you will only have to deal with the surplus once. As soon as you've completed leveling that job, it will cease to affect your gameplay for the entire rest of your gaming experience. (The fact that you say you leveled sub jobs also suggests to me that you would slightly level some jobs in FFXIV to get their abilities for your main job -- something you can be doing when you hit surplus on your main.) You may have only played that one job, but you probably only spent a minority of your gaming career actually leveling that job, with the rest of your experience likely being endgame/crafting/missions/camping/etc. Obviously I don't know your case personally, but I knew a few people who only played one job for their entire career, and that's more or less how it was for them.
I had a feeling someone would ask this:
I didn't play FFXI much during the week, but I would have marathon sessions on the weekends (Fri,Sat, Sun). I hate casting classes. I don't care about crafting. Didn't touch them AT ALL in 11. Didn't touch dragoon. Didn't play Monk past lvl 15. Which means, I can't really play during the week, and after a certain point I can't level my one or two jobs. Besides the fact that I am going to be paying $15 a month and I will be having (IMO) less of an experience than FFXI. Not to mention, I had planned to take my vacation on launch week. I guess I won't have to do that now that I can only lvl my class for ~17 hours.
I personally think this whole system is a cop out. I am against this idea of trying to support two MMOs, which is most likely where this comes from. They have had 5 years to develop this game. The focus on solo gameplay has me a little worried, but I was going to look past that. This is just disappointing to me. I WANT to like this game. ._.