It's unfair to be obscure about things, so here is the deal.
- Your basic group is like a jazz group. You have rhythm, you have the people who carry the tune.
- The rhythm section are your utility classes. They make the group survive/fast/etc. and the mob(s) slow/rooted/mezzed.
- The DDT (damage dealers/takers) are directly harming and/or purposely angering/occupying the mobs in some form of off tank or kite function.
That is basic eq group mechanics. My best take. Like a jazz combo of some sort, things are only interesting when the two sections are tight. You can't script it. The "immersion" of the jazz combo is = the immersion potential of the original eq player.
Ideally, a good number of classes should be able to perform the DDT function, even if inefficient. The rhythm section should be able to figure out how to use two wizards, for example, as the DD(if not T) classes.
All this requires CC mechanics keep apace of other mechanics. Without CC, well, you would have to make healers overpowered for anything but a warrior.
The cascade of problems with eq begins and ends with enchanters. It would be nice to see a simulator that tried to "erase" this problem. It's not classic.
Just like charming.