Cubase is fine for most plug ins such as Ominsphere, performance is comparable to Logic. Kontakt is the one that for some reason after you load about 150 of them or so, Cubase overloads and cannot play back at all - even with empty Kontakts. It’s a shame because Cubase is the best DAW for scoring (I believe) but Logic can load seemingly an infinite number of Kontakts and the CPU use is nothing if no audio is passing through those instruments. The new version of Logic will support 1000 VI tracks (big deal I know 
and if it can manage the CPU in the same way, it’s hard not to argue the Logic is a better option for scoring with huge Kontakt sessions. This is with multi-core off in Kontakt, let the DAW manage that of course.
And yeah, bouncing and exporting in Cubase takes a very long time compared to Logic / Ableton / Bitwig. Bitwig can load 500 VST Kontakts no problem and still have a lot of CPU to spare, is its not an AU vs VST issue.