fix general performance and environmental performance first.
Shaders play an important role in graphical performance. We do not know what they changed, asides from it looking different the code may also have been optimized further to enhance performance. Beyond that, performance is not all too bad. In many areas a 100+ fps is not impossible, and an fps of approx 50 - 60 in warzones is also not out of the question; on highest settings at 1080p.