I just looked at the plague code myself, and I agree. Every single plagued unit is doing 10-radius area checks for allied units to infect every second. With hundreds of units in play, this exceeds even the number of area checks the AI does by a significant factor. Combined with the small overhead from the buff add/removes and the other checks that it does, it's pretty brutal.
This was a very hastily-designed ability.
- The max plagued units number is totally disregarded by the code. Plague from one UB can affect an unlimited number of units. They have code in place to track the number of units plagued, but it's commented out. I don't know if they had problems with it, or if it meant extra overhead that rarely came into play, or what.
- There is no meaningful way to reduce the sim burden of this ability without also reducing its infection area of effect, damage pulse rate, and its overall duration. Any effective fix will have balance repercussions. I personally don't have a problem with this, as it's a fairly terrible skill right now (even disregarding the sim hit).
I think decreasing the infection radius and duration while increasing the damage per second and interval delay should keep the ability fairly balanced overall. It will (potentially, though not practically) infect fewer units due to the longer delay, lower radius, and reduced duration, but should deliver more damage per infection as most infected units are killed off by other sources of damage long before the plague has run its course.
10/15 damage per interval
1 second interval
10 infection radius
1 second infection interval
10dps * 30 = 300
15dps * 30 = 450
Total 30 damage intervals, 30 infection intervals
20/30 damage per interval
1 second damage interval
7 infection radius
2 second infection interval
20dps * 15 = 300
30dps * 15 = 450
Total 15 damage intervals, 7 infection intervals
This should result in less than 25% of the sim work that the original was doing, as the actual damage part is very simple. To put the infection checks into relative terms, the current checks are covering 9500 square units per infectee over the lifetime of the plague. The reduced check time and radius above would cover only 1000 square units per infectee.
Infection will be less rampant, though still more than enough to easily infect entire creep waves in seconds. The moderately increased damage per second should make up for this, while still being well within reasonable thresholds for Demigods at level 10 and 15.