I hope you're aware that the player at the very top are definitely using pots. That alone already boosts your damage significantly.

With that out of the way, you should probably factor in things such as Trick Attack and Balance.

Now maybe they don't do this for Exdeath, but I wouldn't be surprised to see some parties doing a run exclusively so they can give as many buffs to the tank so that they ultimately end up with an abnormally high DPS.

Alright! Now that we've got all of that covered, all that's left are actual rotations! To figure out what the best ones might be, you can use the replay feature in fflogs and it'll show you exactly what skills the players use during the fight, so you can check out and experiment with other people's openers and whatnot. But be warned - just because the highest ranking player is doing it, doesn't mean it'll always be the best. You have to take context into consideration, but this should still give you something to work with.