There's been a certain amount of hate directed towards casters after lag-failed Mabar runs, blaming their AOE spells for the lag.
I've had one successful Mabar run thus far (CR26-30). I've cast AOE spells liberally during that run, and there was no lag whatsoever, so this is not a 100% cause-effect situation. But I cannot rule out the possibility that under some situations, like when mob count or AOE count exceeds a certain number, it could cause lag. On some runs, I've not cast any AOE, but lag still occurs. But of course, AOE spells can be occurring at other altars that I cannot see.
Its been difficult to pin down the cause of lag, because when lag occurs, people don't want to do post-game analysis, and go over what's had happened in the 4 altars. They have either lag-died and are at their bind points, or they have rage-quit, or they just don't want to stick around.
There are alternative rumors spreading around. Like lag occurs when people pull out their pets/summons, or when too many people come into an instance. Another popular theory is that disco balls/CC spells cause lag.
Personally, I think that the most "rational" reason for lag is that when a combination off too many toons and too many gargoyles occur, there is simply too much computational load on the server. The AOE/CC theory of lag is just false correlation, because when too many gargoyles occur, casters intuitively reach for their AOE/CC spells. But I'm not sure.
I'm hoping that this thread will enable some calm postgame analysis to help everyone track down the cause of the lag. Its difficult to do controlled experiments since Mabar is a public instance that anyone can enter, not everyone is willing to do what you ask, and no one person can see all 4 altars. So sociological-type correlations are all we can aspire to.