Hi,
In my opinion, a key problem when going random is, that the instance ID is bound to the one opening it.
In like any other MMORPG it is possible to continue with an instance runs no matter who lefts the group. You can just invite a new guy and all is fine. I have absolutely no clue why you did not implement this basic and well tested concept.
Privileging one player in the group over all others is absolutely not logical. Some ppl search for instances without making sure they even have the usual (optimal speed) time to complete it because they just dont know the instance.
The new lfg tool makes random groups even more risky because setting up a group is less personal and more automated.
To make the lfg system usefull for all dungeons, you should make it possible to obtain the instance id if the group leader leaves (by free will, not by being kicked out…)