Hi, I don't think you need to attack each mob, I usually shield lob one of each group and flash the rest.

When I have problems, it is not because of not keeping aggro, but difficulty to stay alive until all mobs are dead. Flash a lot and circle of scorn once mobs are near you. The result depends a lot on the healer, the DPS, and how you use your cooldowns, avoid AoE, etc. If sometimes all goes well and others not, it is not only your fault, it's the whole group, you might improve something, but it's not only you. The simple fact of trying to do a speed run instead of doing two separate pulls (which I do in normal DF groups) means you are a bit more stressed and more prone to mistakes until you have a lot of experience. It's difficult to avoid AoE at the same time you struggle for keeping agro and recovering mp to be able to flash. Avoiding harm may help, at least for me it's difficult to do while occupied with other things.

In the next pull it is important that nobody pulls the raptor on the left in the bigger room. You pull the first 3 and then go completely right so that the raptor does not aggro you. All members of the group have to take care not to aggro that one. Then you shield lob one of each group and group them all near the second group.

Once I am on place I flash a couple of times, circle of scorn, flash all the mp, then riot blade combo + flash, attacking the mob that seems might lose aggro if there is one, if not, the one you want dead first. If someone gets yellow, which is not frequent, shield lob ( in case it has moved out of normal attack reach) or riot blade combo him.

As I see it, speed runs are not that easy. In a group that has practiced together you get to do it, but with new people it may not go well, at least at first try.