And if you read the third paragraph, it states:
"What we eventually discovered is that the Sylvanas fight in particular is very messaging-heavy, the mechanics involved require sending many frequent updates to the player’s game clients, which in itself isn’t a problem. However, we discovered that an unrelated change to how we organize and distribute server processes across our server hardware, combined with accumulated changes over time to how our hardware server infrastructure is organized, resulted in our server processes being more concentrated across our hardware."
So it's not the scripting that's the problem, it's the hardware infrastructure. It's like putting new tires on your car but forgetting to put snow chains on then thinking your tires are no good.