I can understand that point. Think of it like this though: Tier 1 merits allow us to perform an action specific to our job more times than we could normally. This is why Phantom Roll recast is a no-brainer. Figure this also: in a one hour fight, unmerited, you'll be allowed to use Quick Draw sixty times. This allows for us to do a touch of damage, but more importantly boost debuffs. Fully merited, you can now Quick Draw seventy-two times. It doesn't sound like a lot, but twelve extra quick draws can add up in damage as well as allow you to boost more than one debuff faster.
Or think of it another way: on pulls in Dynamis, where things need constant sleeping, ten seconds on a timer is pretty large. You can do more in the same period of time with a fully merited timer.
Even while pulling in a merit party (and yes I know it's rather undesirable but COR CAN pull extended chains) it becomes valuable, as you can stage mobs faster.
I don't really have inventory problems on COR. I have a set of gear I use for damage subs, and a set of gear I use for mage sub, but I don't carry them on me at the same time, which allows me to swap in AGI for QD much more easily.
I thought I saw somewhere that 1 acc merit = 2 AGI swapped in but I'm not positive...
XI Wiki

