Right off the bat I can say unless you're running double PLD you should never be MTing as PLD. Both DRK and WAR are far better suited for the MT role on that fight and most fights in general. If for whatever reason you have to MT as others have said shirk and provoke are your friend there, along with shadewalker if possible and diversion use on cooldown by your DPS (something I've had to repeatedly request this tier for some reason and usually on deaf ears..). As for decent DPS one of the toughest things for former range players (I assume you mained healers prior to this) is greeding gcds while handling mechanics. Weaving in and out to squeeze in another gcd or leaving too early/not getting close enough to fit another in.

Also, though I haven't played pld in particular this tier you can try to line up your holy spirit/requiescat window for when you have to move to hallowed the stack marker so you don't lose uptime from being on the boss. Your placement when picking up the last kiss can also lead to lost damage if you have people making you come to them away from the boss in order to safely pass it/have it explode. I've seen groups have the ot run as far as the gate and have them stay there to handle that mechanic leading to quite a few lost gcds over the course of a fight.

Raid composition is a factor as well, having a well structured group with all the damage buffs can really add up. In general though it's the uptime that will make or break your dps so try to keep active for most of the fight and compare your CPM to other players who are parsing higher. As long as your uptime improves your damage will improve.