I'm staying away from the main part of this discussion now, because I've already covered all of what I feel are the major points (several times!)
But I'm a PLD with Standard Relic, Full DL accessories (besides the Hero's Ring), and Valor Head and Body. I sit at over 6k HP in a party without food. (Before I had my Valor Head + Body, it was just shy of 5.8k...) Last week I cleared Turn 4 in a PUG, with just NQ Knight's Bread.
Seriously, Turns 1-4 aren't rocket science. They just take a tiny bit of practice and the ability for most of your team to be able to dodge on command.
If I can clear Turn 4 in a PUG with a little over 6100HP, there's no reason at all that a i90'ed PLD with Melded Gryphonskin accessories sitting at over 6500HP should be having the slightest bit of trouble at anything lower than Turn 5 with a static group. ("BIS" to me implies your other slots are already pretty damn good and you're looking to tweak your build as much as possible for best performance... I'm not sure I'd recommend someone spend all their gil on melded Gryphonskins if they're still running around in AF or Hoplite armor pieces...)
Sorry, but Paikis is right here.
If you go the EAST route on Turn 2 then ADS takes 25% reduced slashing damage (Tanks) and 25% reduced Magic damage (BLM and SMN). The damage of other DDs - for example Bards - is unaffected. That basically means a 25% enmity buff for the other DDs. Melded Gryphonskin accessories increase your tanks damage output (over +Vit accessories) by about 20-25%, which almost completely closes that gap.
Our FC group has a heck of a lot of Bards. It means we've got plenty of silencers for ADS, but hate is definitely a little bit trickier to hold if we go that Eastern route because the bards occasionally like to blow all their +DMG/+Crit cooldowns simultaneously and tend to forget about Quelling Strikes.
If you go the WEST route, then Tanks deal normal damage and enmity is a heck of a lot easier.
It's also a little trickier to build hate on Turn 2 ADS, because you're not quite able to generate a constant stream of RoH combos on it - whenever the tanks swap positions, the first tank needs to hold back a bit on aggro generation until hate is properly traded.
It's not that tough a fight (dodging and silence timings excepted) but the aggro mechanics aren't as straightforward as with "normal" bosses.
In CoH, for a long time the main raid mob in the game (Hamidon) could be tanked by a single DPS class (Regen Scrapper) whilst over 200 people wailed on the boss.In RIFT
Other MMORPG's mechanics are fun...
(Also, it has been stated that Coil was intended for i80 gear - the drops from Crystal Tower. Darklight is i70. Allagan/Myth is i90. This means that a mix of both is pretty much "balanced" for Coil, but just wearing Darklight is technically being undergeared.)