Cubase Multicore OSX. Is there an issue?

Definitely not a good spread over the cores here.
I am on a Mac pro 2013 6 core. A 88.2 project with approx 70 tracks and not exceptional amount of plugins is starting to stutter. Asio meter at approx 90% and hitting red. CPU meter of Mac at 6%

Selecting highest buffer size helps a little bit but not much.

I know Asio performance is not the same as CPU usage but what is the limiting factor here?