But it's not random. If there is code that is supposed to inherently favor the makeup of the group, it no longer becomes "random".
The Oxford English Dictionary defines random as "Having no definite aim or purpose; not sent or guided in a particular direction; made, done, occurring, etc., without method or conscious choice; haphazard.". Obviously this is not the case. However, one can argue that it isn't working very well.
I suggest reading into statistics and probability. Unless you can define the actual probability that an individual drop will occur with a specific group composition, from out point of view it will always be random. I've already tested loot drops in HM's (ran many HM runs with a full bounty hunter comp) and I can say that there is a bit of sway in the drops. But that sway is not going to be very noticeable when it comes to situations where three or even two classes are present.