The dev team responds about your concerns regarding Scenario performance issues:

We have been listening to the Warhammer Community about performance issues players are having while they were in scenarios. While we had the servers down today, we applied a number of fixes designed to improve play in scenarios and make the experience better overall. Our goal is to make scenarios the best possible experience for our players.

Be sure to let the devs know of any additional concerns you have through their feedback form . There is also a forum discussion here to talk about the changes.