I know people in this thread are busy screaming about how it tells you this. But honestly it really should be a character slot and not just the character that is bought with the ticket, excuses of well the JP version does this too, don't float either I never said they don't, but I still think it should be changed in general. I have bought a character knowing how this works and don't plan on deleting them, so I am not a person that knows nothing about this.
If the items, meseta, etc, that you can get from remaking the character is the only issue there are other ways to prevent this while still making these an actual slot. They could make the slots turn into a placeholder instead of the slot being replaced if you buy another ticket after deleting the previous character, and make it so that any character created in that spot has the mag box mission marked as already completed (and give no reward for it) so you cannot reclaim it, and for the weekly client orders also mark them as already completed so you can't get the meseta reward that week.
Or they could do a less preferable way and still do the mag box thing and make you wait a week to recreate a character in that slot.
I don't get people that refuse to acknowledge that it really shouldn't be done this way, because it being a slot you're getting and not just the character can only benefit people. You know how this works you didn't make this mistake? So what it shouldn't be this way just because it is now.