Most importantly, these debuffs need to be RED MAGE ONLY Sharing them with other jobs is what takes our specialty away from us, SE. Saboteur is not enough to handle this issue.
We're probably going to get Addle II and Suchandsuchnewdebuff II in the next line of merits (who wants to bet Gravity II is going to be in there?). And to them, that's what makes it all A-OK. Even though it will boil down to meriting what is most efficient as opposed to having the full range of new spells and not having to choose at all.

Let's face it. None of us worth our merit chose to learn Blind II. But if I didn't have to choose at all, absolutely I would use it because there would simply be no reason not to. If you ask me, I say they just remove the Category cap on Category II merits and let everybody learn all of their abilities/spells/traits.