Marking can be handy, but it is *not* needed by any stretch. You are using it as a crutch for yourself and hand-holding your dps. You are giving advice to others based on your own self imposed limitations. This behavior makes you look like a narrow minded boy, not knowing what he's talking about. (Turnabout is such fun, isn't it?)
I've never marked, nor needed to mark, anything in any dungeon at any level. I do not lose aggro. I do not care what the dps choose to hit. I do not complain anyone has "hit the wrong target". I have never failed a dungeon run.
Only twice have I had dps that complained they wanted marks. I informed them they were free to mark or organize amongst themselves as they saw fit and that was that. Some tanks might want/need marks, they will have to try them out and decide for themselves what it is that works best for them.
As far as advice. After rounding up your targets you will want to flash or overpower at least 2 to 3 times to secure enmity over the healer and gain some time to assess the situation. While you are doing that glance at the enemy health in the enmity listing to see which is dropping fastest. This will give you an idea where to start putting your threat combos. You will want to cycle through the targets and look at the small white bars to the left of your group's health bars to see how much threat each group member has on each target.
If multiple targets are being hit faster then you can build single target enmity, or if you have pulled more targets then you can easily cycle through, you will want to continue with overpower and/or flashes. As flash/overpower are area effects the target you have selected matters little so you can also use this time to cycle through and make sure none of your group members are getting close to taking aggro despite the AE. If the enmity bars are all low you can slow it down so your TP/MP isn't drained for the next fight. You will learn how much you need to AE in a given situation with practice.
As far as doing low damage... It is the primary job of the dps to work down then enemy health bars. It is your primary job to work down your group's white enmity bars. While it helps things along to do as much damage as you can get away with that is not your primary role. Similarly it helps things along when the dps is aware of their enmity.
It might also behoove you to learn to gauge the range on flash as opening with a flash *just* as the mobs get into your range can be a handy habit to get into. Sometimes the healer will cast something on you mid-pull and suddenly the mob are running right past you. That opening flash will intercept them even if that happens.