My personal opinion as always.
Optimizing applications to improve performance is time consuming and costly. Helms Deep will increase the size and complexiity of the Lotro software. I expect performance will go down.
Typically what happens on the applications I work on a major release reduces performance. We have to analyze and release changes to the software to improve performance before the next major release. Or we sometimes we decide there is nothing we can do about the degradation because the only way to fix it is to remove the new features which is not happening.
Our goal is to try our best to hold the line when a major release occurs by minimizing the degradation.
Unless stated otherwise, all content in this post is My Personal Opinion.