Generic section merits are pretty much capped. I am mainly concerned about DRK specific merits. Been changing around a few things lately, which is why I've been meriting again. The following is what my build is now starting to look like.
Souleater Recast 5/5
Last Resort Effect 5/5
The reason I went Souleater recast over Last Resort is so they would have the same timer. Souleater starts at 6 minutes so full merits would bring it down to 5, which combos with Last Resort which starts at 5.
Dark Seal 5/5
Diabolic Eye 5/5
I realize the lack of enmity down from muted soul but I figure even with muted soul I would probably still end up tanking when I pop Dark Seal > Drain II > Last Resort > Souleater > WS every five minutes. To combat this, I use dread spikes just before I do that combo to hedge my bets so to speak since that runs on a 3 minute timer. It's not perfect but shadows usually covers me until it all goes off and at that point it's just trying to stay up until someone pulls hate off me.
Diabolic Eye is really there for the times when ACC might be a stretch. At that point the -15% Max HP is sometimes offset by the Drain II. I also do it sometimes on NMs where I would be using Carbonara to give extra HP and ATK, comboed with Drain II Dark Seal it's not terrible HP loss.
I see a ton of people going Desperate Blows 5/5 so that might be something I should look into. I just figured that it wouldn't be that great since Last Resort is only 30 seconds but by the overwhelming support of it, it seems like something I should consider if nothing else for zerging.
It's easier to keep tabs of if they have the same timer. Also, it seemed better to have SE down by a minute than LR by 50 seconds.
Info on 1h and 2h zerg comparisons if that's what you're interested in.
http://ffxi.allakhazam.com/db/jobs.html?fjob=6;mid=1218312631147257222;num=11;page=1
Yeah, in retrospect Dark Seal will probably go the way of the dodo when I get back around to T2 DRK merits.
Sure, you'll have another good chunk of HP when you start the zerg proper. But you'd only really need Dark Seal to land Drain II on the mob you're zerging, and it takes three seconds to cast. Most zergs, as Ice mentioned, are over in thirty seconds. So you're sacrificing 10% of your zerg time to pull the Drain II off, unless people are willing to let the DRKs do a coordinated Dark Seal/Drain II at the start of the fight, and in my experience, it's a needless little fillip on a process that already has a number of steps that can go wrong.
If you did the job right, the mob is going to be dead in ~30 seconds regardless, so you might as well put the merits into something that helps you in other areas.
Note that I did not say anything about the time required to use Dark Seal. I assume that anyone zerging is smart enough to at least do that in advance.
Statistically, given what the average Drain II will do to a mob that's high enough to need Dark Seal to land it, it's just about a null-value assuming that the zerg lasts 30 seconds. You'll pick up about as much from Drain II and the added damage as you'll lose in the 3 seconds it takes to CAST it. If the fight goes longer than 30, of course, it's worthwhile.
So it really depends on who you're playing with, and precisely what you're doing. In my case, we've got enough good zerg builds in iiZerg (ironically enough) that sometimes the mobs don't even last the full 30 seconds. I've had instances on KV where I've hit my Drain II and the mob was dead before I got 15 swings in with a Mercurial Kris.