The aoe rot IMO made it more difficult for blizzard to balance between single target and aoe while maintaining any sense of theme.
If they buffed rapture strong enough to be useful and impactful in 2s, it would make affliction godlike in 3s. If they buffed shadowbolt and haunt enough for that, it would result in affliction having a great deal of burst without even consuming soul shards.
I think the very best part about this change is that it provides a tuning-knob for aoe and ST independently.