I see lots of posts suggesting three heals, I really don't think that's the way to go. I feel 1 tank, 2 heals (SCH + WHM), 5 DPS is the most optimal build. This is what I used to kill titan for the first time (no one in my group had relics) and this is what I use to sell Titan runs (minus 1 DPS for whatever the carry is).

I also disagree with the statement that one bad player can ruin it for 7 others, that's just simply not true, if it was there wouldn't be anyone selling titan runs.

The most important thing to worry about on Titan is the Mountain Buster, with no CD / Virus, it hits for around 3.5k - 4k damage, and there is usually a melee hit right before it too. In short there needs to be something on the tank for it everytime. If you hadn't figured it out, he always does a set rotation after the heart phase. Without going into too much details, the tank hit is ALWAYS right after Landslide, when you see landslide you know it's time to get a CD up. It also helps if the tank is very vocal about calling out CD usage and when he needs healer buffs (virus / sanc). Also, I'm not sure what the bench mark is for MRD, but your PLD should have over 5k health.

Other than that, the only things that will kill you is probably rock mines or weight of the land. For weight of the land we always lined up in a straight line behind the boss and then spread when weight came up, this seamed to work best for us. For mines learn the patterns, when he drops them in lines the middle is usually always the first, so just go to one of the sides and then go mid right after it blows up.

Hope this helps a little , also it's crazy how much easier it is to kill after you kill it once.